what are atoms help

What Are Atoms Help

Answers

Answer 1

a b c d no a no b yes c no d ok


Related Questions

Select all that apply.

How may the concentration of chloroform be increased as Cl2 gas reacts with CH2Cl2?

increase [HCl]
remove HCl from the product
increase [Cl2]
the rate of reaction cannot be changed

Answers

Answer is:increase [Cl₂] and remove HCl from the product.
Chemical reaction: Cl₂ + CH₂Cl₂ → CHCl₃(chloroform) + HCl.
According to Le Chatelier's Principle, the position of equilibrium moves to counteract the change, the position of equilibrium will move so that the concentration of reactants decrease (Cl₂) and concentration of products of chemical reaction increase (CHCl₃) if increase concentration of reactants and decrease concentration of products.

 


Answer:

increase [Cl₂]

remove HCl from the product

Explanation:

Odyssey ware

A 250-mL aqueous solution contains 1.56 10–5 g of methanol and has a density of 1.03 g/mL. What is the concentration in ppm?

Answers

First, calculate for the mass of the aqueous solution by multiplying the given volume (in mL) by the density (in g/mL). In mathematical equation, that is,

        m = ρV

where m is mass, ρ is density, and V is volume. Substituting the known values,

      m = (1.03 g/mL)(250 mL) = 257.5 g

To get the concentration in ppm, divide the given mass of methanol by the mass of the solution. Note that the parts-per million (ppm) is equal to mass of solute in milligram(mg) divided by the mass of solution in kilogram (kg)

      C (in ppm) = (1.56 x 10^-6 g)(1000 mg/1 g)   / (257.5 g)(1 kg/1000 g)

Simplifying,
     C (in ppm) = (1.56 x 10^-3 mg)/ 0.2575 kg

     C (in ppm) = 0.00606 ppm

Answer: 0.00606 ppm
     
Hello user

Answer: Answer: 0.00606 ppm

Hope I helped
-Chris

At the top of a mountain, the pressure is found to be 0.52 atmospheres. How does this compare to standard atmospheric pressure at sea level?

Answers

14.70 psi at sea level

1.000276 atmospheres at sea level

Hope this helps
:)

Answer:

It is less than(almost half) the atmospheric pressure at sea level.

Explanation:

When we move up high , the pressure decreases with increase in altitude.

The pressure or atmospheric pressure is due to air present.

As we move up, with the altitude the amount of air decreases which cause a decrease in atmospheric pressure.

If the pressure found to be 0.52 atm at the top of mountain it is due to higher altitude.

This is less than the normal or standard atmospheric pressure at sea level which is 1013.25 mbar or 1 atm.

.817g of an unknowm gas occupies 1.25L at 27.0°C and a pressure of 765 mmhg. is the gas most likely methane(CH4), ethane(C2H6), propane(C3H8), or butane(C4H10)? please show work.

Answers

Use the equation pv=nrt

101991.60949Pa(0.00125m^3)=n(8.31)(300°K)
n=(101991.60949Pa*0.00125m^3)/(8.31*300°K)
n=0.0511moles

You have grams, which is .817, and you have moles. The next step is molar mass.

.817g/.0511moles=15.988g/mol

Now, calculate the molar mass of each gas.
CH4 = 16.043g/mol
C2H6 = 30.07g/mol
C3H8 = etc
C4H10 = etc

The closest answer is your CH4 (methane), so that is your answer. Hope this helps!

P.S. If you wouldn't mind, if you could mark this answer as Brainly so I can keep moving up levels! Thanks :)

Match the receptors with their motor responses?

Answers

Optic receptors get stimulations from vision by eyes.
A person stopping at a red traffic light due to that person gets the vision signals by optic receptors.

Auditory receptors are stimulated by hearing sounds by ears.
A student giving an answer in response to a verbal question is because of the auditory receptors.

Photoreceptors are stimulated due to the light.
Example: a sunflower turns towards the light due to the photoreceptors.

Skin receptors can feel touch, temperature and pain.
Hence, a cat's fur rising when touched due to the skin receptors.


why the element in periodic table which have more than three electron valens must plus ten in order to know the group in periodic table ?

Answers

Answer:-

If an element has 3 or more valence electrons then the element belongs to p block of the periodic table. For p block elements the group number is found out by adding the number of electrons in valence shell + 10.

The reason for this is because in the middle of the periodic table there are the d block elements ranging from group 3 to group 12 a total of 10 groups in between elements having 2 valence electrons and 3 valence electrons

The volume of a gas is doubled while the temperature is held constant. How does the gas pressure change

Answers

As the volume of the container increases, the gas pressure decreases. They are directly proportional. This is supported by Boyle's Law.

Answer: The new pressure will be half of the original pressure.

Explanation:

To calculate the pressure change, we use the equation given by Boyle's law. This law states that pressure is inversely proportional to the volume of the gas at constant temperature.

The equation given by this law is:

[tex]P_1V_1=P_2V_2[/tex]

where,

[tex]P_1\text{ and }V_1[/tex] are initial pressure and volume.

[tex]P_2\text{ and }V_2[/tex] are final pressure and volume.

We are given:

[tex]V_2=2V_1[/tex]

Putting values in above equation, we get:

[tex]P_1\times V_1=2V_1\times P_2\\\\P_2=\frac{P_1\times V_1}{2V_1}\\\\P_2=\frac{P_1}{2}[/tex]

Hence, the new pressure will be half of the original pressure.

Name at least two Benefits of using models in science

Answers

They provide a way to understand the processes that might otherwise be outside the scope of humans. Also they provide scientists with foundations for further experiments and hypothesis.

Answer:

Models make concepts more tangible. They also make it possible to notice patterns, develop or revise representations, and predict or explain events or relationships.

Explanation:

Trust me it's the answer okay

The energy that is available to do work in a reaction is called

Answers

Free energy
I hope that helps (:

Which information is represented by a line on this map?

A. points with the same elevation

B. the location of a road

C. a direction north or south

D. a direction east or west

Answers

The correct answer is:  [A]:  "points with the same elevation" .
________________________________________________________


A scientist did an investigation on the growth of koi fish. He selected forty newly hatched koi from the same clutch of eggs. He separated the koi into four groups and placed each group in a different sized pond. None of the ponds had any predators that would eat the koi fish. The amount of food available to the koi and the water quality of each pond differed based on the size of the pond. Larger ponds had more food available and better water quality as the fish grew.

After 15 months, the scientist measured the length of each koi fish. Using these measurements, he came up with an average koi size for each pond.

Effect of Pond Size on Koi Fish Growth

Size of Pond Average Length of Koi
500 gallons 18.2 centimeters
1000 gallons 25.6 centimeters
2500 gallons 30.8 centimeters
5000 gallons 35.3 centimeters

Based on the scientist's results, which of the following is true?
A.
Koi fish grow fastest in ponds with poor water quality.
B.
Koi fish grow fastest in ponds with a high population density.
C.
The growth of koi fish is determined entirely by genetics.
D.
The growth of koi fish is affected by the environment of the fish.

Answers

Answer:

d

Explanation:

just did it

From the results, it is clear that, the growth of the koi fish is depending on the environment in which it grows. This include, the size of pond, food available, water quality, presence of predators etc. Hence, option D is correct.

What are environmental factors affecting fish growth ?

The condition of the water in which fish are grown directly affects their health and eventual growth. In general, physical, chemical/biochemical, or a combination of these components can be used to categories factors impacting fish growth and productivity in freshwater aquatic systems.

Temperature and suspended and settleable particles concentrations are significant physical water characteristics for the development and growth of fish; crucial chemical water characteristics include pH, alkalinity, hardness, and metal concentrations.

The adequate size of pond let the fish free to move more and make it more energetic with the surroundings. Hence, the growth of koi fish is affected by the environment of the fish.

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The modern periodic table arrangement is a result of all of the following except many scientists who contributed individual knowledge. total rejection of the early versions for modern ideas. much scientific reexamination and argumentation of ideas. periodic repetition of the chemical and physical properties of the elements.

Answers

The correct option is this: TOTAL REJECTION OF THE EARLY VERSIONS FOR MODERN IDEAS.
The modern periodic table arrangement was as a result of many contributions from many scientists, who contributed individual knowledge. The periodic table has gone through a lot of reexamination and it is always regularly updated as new scientific facts emerge. The elements in the periodic table are arranged based on the periodic occurrence of the chemical and physical properties of the elements.


What energy transformations occur between the microwave oven and the meal? *

Answers

Electrical energy turns into thermal, sound, radiant, and mechanical energy (all kinetic)

How many grams of O2 can be prepared from 4.50g of KCIO3

Answers

93.9 grams of KClO3(s).

Final answer:

The amount of O2 that can be prepared from 4.50 g of KCIO3 is calculated using stoichiometry. From the balanced chemical equation of the reaction, we find out that we can expect 1.008 grams of O2.

Explanation:

The question asks about the amount of O2 that can be prepared from a certain amount of KCIO3. This is a chemistry question involving stoichiometry, which is a section of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction.

For this reaction, the balanced chemical equation is 2KCIO3 → 2KCl + 3O2. From this, we can see that from each mol of KCIO3, we can obtain 3/2 mol of O2. The molar mass of KCIO3 is approximately 214.55g/mol. So, 4.50g of KCIO3 equivalents to 4.50g/214.55g/mol = 0.021 mol. According to the balanced equation, these 0.021 mol of KCIO3 would produce 0.021 mol * 3/2 = 0.0315 mol of O2. Considering that the molar mass of O2 is 32.00 g/mol, the mass of O2 produced is 0.0315 mol * 32.00g/mol = 1.008g.

Therefore, the amount of O2 that can be prepared from 4.50 g of KCIO3 is approximately 1.008 grams of O2.

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Which of the following is a substance made up of only one type of atom?

Answers

A pure substance is something that occurs in nature. An element is made up of one type of atom only and cannot be split further. A compound has the combined properties of the elements from which it is made. Atoms show the macro properties of an element. 

Answer:

element

Explanation:

also you stole that answer off some other guy

Name the 5 types of chemical reactions

Answers

There are way more than 5 but I will list the ones I know:

Reaction with acid

Reaction with water

Combustion/Flammability

Combination

Redox

Isomerization



Final answer:

The five types of chemical reactions are acid-base reactions, exchange reactions, condensation reactions, cleavage reactions, and oxidation-reduction reactions. Examples of each type of reaction are provided.

Explanation:

Most chemical reactions can be classified into one or more of five basic types: acid-base reactions, exchange reactions, condensation reactions (and the reverse, cleavage reactions), and oxidation-reduction reactions. Examples of each type of reaction include:

Acid-base reactions: When an acid reacts with a base to produce a salt and water. For example: HCl + NaOH → NaCl + H2OExchange reactions: When two compounds react to form new compounds by exchanging one or more atoms or ions. For example: AB + CD → AC + BDCondensation reactions: When two small molecules combine to form a larger molecule and also release a small molecule as a byproduct, such as water. For example: A + B → AB + small moleculeOxidation-reduction reactions: When there is a transfer of electrons between reactant species. For example: Fe2+ + Ce4+ → Fe3+ + Ce3+

How are elements arranged in the Periodic Table? A. by their properties B. alphabetically C. by how much they are worth D. in the order they were discovered 2. (10 pt) Which is the correct symbol for the element silicon? A. SI B. S C. Si D. Sil 3. (10 pt) All atoms of an element are ________ . A. flammable B. visible under a microscope C. alike D. different 4. (10 pt) Elements that are usually shiny and good conductors of heat and electricity are known as ________________. A. gases B. metals C. solids D. nonmetals 5. (10 pt) The most recent model of an atom is the _______________. A. Bohr model B. Einstein model C. Nucleus model D. Electron Cloud model 6. (10 pt) Elements that are usually dull, brittle, and do not conduct electricity are known as A. gases B. metals C. solids D. nonmetals 7. (10 pt) Elements join together to form A. compounds B. ions C. protons D. atomic masses 8. (10 pt) Which picture best shows an atom? A. B. C. D. 9. (10 pt) In order for a chemical reaction to take place, a certain amount of _______________ must be present. A. heat B. friction C. chemicals D. energy 10. (10 pt) Enzymes are ____________ in the body that speed up chemical reactions. A. catalysts B. cells C. concentrations D. chloroplasts

Answers

Answer:

In the modern periodic table, the elements are listed in order of increasing atomic number. The atomic number is the number of protons in the nucleus of an atom. ... In a periodic table arranged in order of increasing atomic number, elements having similar chemical properties naturally line up in the same column

Explanation:

I hope this helps

Final answer:

The Periodic Table is arranged by their properties, with elements grouped according to similar chemical and physical characteristics. Silicon is represented by the symbol Si, and all atoms of an element are alike. Metals are shiny and good conductors, while nonmetals are dull and poor conductors.

Explanation:

1. Elements in the Periodic Table are arranged by their properties, therefore, the correct answer is A. by their properties.

2. The correct symbol for the element silicon is C. Si.

3. All atoms of an element are alike, meaning the correct answer is C. alike.

4. Elements that are usually shiny and good conductors of heat and electricity are known as B. metals.

5. The most recent model of an atom is the D. Electron Cloud model.

6. Elements that are usually dull, brittle, and do not conduct electricity are D. nonmetals.

7. Elements join together to form A. compounds.

8. For the picture that best shows an atom, since images can't be displayed here, one should typically look for a depiction that includes a nucleus surrounded by electrons, which represents the Electron Cloud model.

9. In order for a chemical reaction to take place, a certain amount of D. energy must be present.

10. Enzymes are A. catalysts in the body that speed up chemical reactions.

How many atoms of copper will react with 33.9 L of nitrogen stp to produce copper nitride

Answers

Hello user


Answer: 33.9 L of N₂ will react with 576.96 g (9.08 moles) of Cu.

I hope I helped 
-Chris

Answer : The number of atoms of copper will be, [tex]54.67\times 10^{23}[/tex]

Solution :

As we know that 1 mole contains [tex]6.022\times 10^{23}[/tex] number of atoms

And,

At STP, 1 mole contains 22.4 liter volume of gas

First we have to calculate the moles of copper.

The balanced chemical reaction will be,

[tex]6Cu+N_2\rightarrow 2Cu_3N[/tex]

From the balanced chemical reaction we conclude that, 1 mole of nitrogen gas react with 6 moles of copper.

As, 22.4 L volume contains 6 moles of copper

So, 33.9 L volume contains [tex]\frac{6}{22.4}\times 33.9=9.08[/tex] moles of copper

Now we have to calculate the number of atoms of copper.

As, 1 mole of copper contains [tex]6.022\times 10^{23}[/tex] number of copper atoms

So, 9.08 moles of copper contains [tex]9.08\times (6.022\times 10^{23})=54.67\times 10^{23}[/tex] number of copper atoms

Therefore, the number of atoms of copper will be, [tex]54.67\times 10^{23}[/tex]

What’s the molar mass of Lead-208

Answers

Lead is a basic metal and almost 11 isotopes of Lead are reported. The isotopes with greater natural abundance are as follow;

1) ²⁰⁸Pb with abundance 52.4 %

2) ²⁰⁶Pb with abundance 24.1 %

3) ²⁰⁷Pb with abundance 22.1 %

4) ²⁰⁴Pb with abundance 1.4 %

Molar mass of ²⁰⁸Pb:

Molar mass of any element is the total of number of protons, neutrons and electrons.
As, number of protons in Lead are 82 then in ²⁰⁸Pb isotope number of neutrons are...

# of Neutrons  =  M.mass - # of protons

# of Neutrons  =  208 - 82

# of Neutrons  =  126

Result:

Molecular Mass of Lead (²⁰⁸Pb) is 208 amu.

# of Protons in ²⁰⁸Pb  = 82

# of Neutrons in ²⁰⁸Pb = 126

Why do onions make you cry?

Answers

When you cut an onion, it releases a gas, when mixed with certain enzymes in the onion, it creates a sulfur gas. These gases then get to your eyes and create a mild acid which irritates the eyes. Hope this helps, if you have any questions please feel free to message me ;)
Final answer:

Onions make you cry due to a chemical process that occurs when they are cut. The broken cells react to produce a gas which reaches your eyes and stimulates tear production.

Explanation:

The reason onions make you cry is because of a chemical process that occurs when we cut into them. Onions contain substances known as sulphoxides. When an onion is cut, the cells are broken open and react with the sulfenic acids to produce a volatile sulphur compound called propanethial S-oxide. This gas diffuses through the air and eventually reaches your eyes, where it reacts with the water to form a diluted sulfuric acid. This burning sensation triggers the eyes to produce tears to flush out the irritant.

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Which nonmetallic mineral is used as a building material and also in the manufacture of steel

Answers

Answer: limestone

Explanation:

What is the difference between creep and a landslide?

Answers

Creep is somthing you might call somone following you. Example, "he was slowly creeping up the stairs behind me". A land slide normally moves faster then that.

A creep is a slow downhill movement of weathered rock material.

A landslide is a sudden movement of rock and soil down a slope.

Basically, creeps are slower than landslides.

Will mark as Brainliest.

For the balanced equation shown below, if 84.7 grams of H2S were reacted with 78.4 grams of O2, how many grams of H2O would be produced?
2H2S + 3O2 → 2SO2 + 2H2O


12.4 grams of water


24.9 grams of water


29.4 grams of water


Please explain your answer.

Answers

Molar mass of H2S = 2M(H)+M(S) = 2*1.0+32.0=34.1 g/mol
Molar mass of O2 = 2*M(O)=2*16.0=32.0 g/mol
Molar mass of H2O = 2M(H) +M(O) = 2*1.0+16.0 = 18.0 g/mol

84.7 g H2S*1 mol H2S/34.1 g H2S ≈2.48 mol H2S
78.4 g O2*1 mol O2/32 g O2 =2.45 mol H2S

                                                2H2S +           3O2 → 2SO2 + 2H2O
from reaction                       2 mol              3 mol
from the problem                2.48 mol      2.45 mol

As we can see O2 is limiting reactant, so we are going to find amount of water using O2 data.

                                         
                                                2H2S +           3O2 → 2SO2 +       2H2O
from reaction                                               3 mol                         2 mol
from problem                                              2.45 mol                    x mol

x=(2.45* 2)/3≈1.63 mol H2O

1.63 mol H2O*18 g H2O/1 mol H2O ≈29.34 g H2O

The answer is   29.4 grams of water.

what acid and base form Ca3(PO4)2

Answers

Base is Ca(OH)2.
Acid is H3PO4.

First part of the salt comes from base, 
second par comes from the acid.

The acid and base that formed the salt [tex]Ca_3(PO_4)_2[/tex]  would be phosphoric acid ([tex]H _3PO _4[/tex]) and calcium hydroxide ([tex]Ca(OH)_2[/tex] respectively.

Formation of salt

Salts are usually formed from neutralization reactions. That is, reactions involving acids and bases to produce salts and water.

In order to form [tex]Ca_3(PO_4)_2[/tex]  from an acid and a base, such an acid must be phosphoric in nature while the base must be calcium-based.

Thus:

          [tex]Ca(OH)_2 + H_3PO_4 --- > Ca_3(PO_4)_2 + H_2O[/tex]

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if you have 100g of a metal heated to 100° then dropped into 100g of water at 22° and the water temp increased to 35° does the metal release heat abosrb heat or stay the same

Answers

release heat, since the water absorbs the heat because it gets hotter.

What’s the IUPAC name for CH2=C(CH2CH3)2?

Answers

Answer:
            The IUPAC name of given compound is 2-Ethyl-1-Butene.

Explanation:
                   First of all, a longest chain containing a double bond was selected as a parent chain, as it has four carbon atoms and a double bond at position 1, so parent name is,
                                               1-Butene

Ethyle (CH₃-CH₂-) is the substituent present at position 2. So, complete name will be as follow,

                                         2-Ethyl-1-Butene

can also be written as,

                                         2-Ethylbut-1-ene
Final answer:

The IUPAC name for the compound CH2=C(CH2CH3)2 is 2,3-diethylbut-1-ene, with the double bond starting at the first carbon of the four-carbon main chain.

Explanation:

The student is asking for the IUPAC name of the chemical compound with the molecular formula CH2=C(CH2CH3)2. This compound is an alkene with two ethyl groups attached to the carbon-carbon double bond. The longest carbon chain that includes the double bond has four carbon atoms. Therefore, the base name is butene. Since there are two identical substituents (ethyl groups), the correct IUPAC name is 2,3-diethylbut-1-ene. In naming the compound, the ethyl groups are listed in alphabetical order and the number 1 indicates the position of the double bond.

5.
The diagram illustrates part of the carbon cycle.


Which best describes the diagram?







A consumer is obtaining carbon by breathing it in from the atmosphere.

A consumer is obtaining carbon by absorbing it from the soil.

A consumer is obtaining carbon by eating carbon-based molecules stored in a producer.

A consumer is obtaining carbon by eating carbon-based molecules stored in a decomposer.

Answers

Answer:

The correct answer is "A consumer is obtaining carbon by eating carbon-based molecules stored in a producer".

Explanation:

The animal is consuming the carbon present in the molecules stored in the grass. Plants process the carbon present in the soil along with other minerals. The animal, when it feeds on these plants, is consuming the carbon they obtained from the soil. Grasslands are defined largely by their use for grazing, which includes between 10 and 30 percent of soil carbon worldwide.

Have a nice day!

Answer:

C

Explanation:

it was right on (edge nuity)

the rows on the periodic table correspond to

Answers

An important point about the columns is that the number of electrons in the outer energy level, called valence electrons, will be the same for all the elements in that column. The periodic table is designed so that the first electron starting a new energy level starts a new row on the far left.

The plant structure that helps transport water and nutrients from the roots to the leaves and other parts of the plant is

Answers

The answer is Xylem. The plant structure that helps transport water and nutrients from the roots to the leaves and other parts of the plant is Xylem.  In vascular plants, plants that have TUBELIKE STRUCTURES that carry water, nutrients, and other substances throughout the plant have xylem (vascular tissue that carries water upward from the roots to every part of a plant) and phloem (vascular tissue tubelike vessels that transport sugar made in photosynthesis from leaves to plant).

The answerto your question is Xylem

How does the radioactive isotope C-14 differ from its stable counterpart C-12?

Answers

C-14 has 2 more neutrons than C-12

C-14
6 protons
8 neutrons

C-12
6 protons
6 neutrons

Isotope  is defined as atom of same element with same atomic number but different mass number.

Here, atomic number for C-14 and C-12  is 6 but mass number is 14 and 12 respectively.

Atomic number is equal to number of protons and electrons in an atom and mass number is equal to sum of number of protons and neutrons in nucleus of an atom.

[tex]A=n_{p}+n_{n}[/tex]

Since, both have same atomic number, the number of protons will be 6 for both but they have different number of neutrons.

Number of neutrons in C-12:

[tex]n_{n}=12-n_{p}=12-6=6[/tex]

Number of neutrons in C-14:

[tex]n_{n}=14-n_{p}=14-6=8[/tex]

The number of neutrons in C-12 is 6 and that in C-14 is 8. Therefore, isotope C-14 differ from the stable C-12 in number of neutrons.

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when the contents of a vesicle are released by the cell ? All cells contain a phosphate buffer system within their internal fluid to help maintain a constant pH. This system can be summarized by the following chemical equation: H2PO4- (aq) H+ (aq) + HPO4-2 (aq) This system mostly contributes to which of the following cellular activities A. maintaining homeostasis B. reproduction C. natural selection D. acquiring energy What did lenin do upon his return to russia in april of 1917? The time it takes me to wash the dishes is uniformly distributed between 10 minutes and 15 minutes. what is the probability that washing dishes tonight will take me between 11 and 13 minutes? Write the equation of the line with the following characteristics.A horizontal line through the point (0,3) What is the Value of Y? If you divided 26 objects into sets of 6, how many sets of 6 could you make, and how many are left over? Ender uses the jeers of the onlookers as a teaching tool. what does this reveal about the character of ender? Find the relative rate of change of the function f(x)=150-0.08x^2 How does HIV/AIDS affect the economics of Africa? When north korean communist leader kim il sung attempted to reunify korea under a communist government by invading the south, how did the us government respond? Laura recently ended a 10-year relationship when she learned her partner was cheating on her. the situation most likely caused ____________ work problems exhaustion distress. eustress Zola is very skilled with Microsoft and Apple, and she knows different methods of programming. This knowledge will help make Zola a successful candidate for a Hospitality and Tourism career. Which type of qualification does she have?A}professional appearanceB}flexibility in handling unexpected tasksC}good computer skillsD}expertise in problem solving Please answer and explain What is the value of x? sin(x+21)=cos(2x+21) given a mean of 7.6 and a standard deviation of 3.1 what is the z-score of the value 10 rounded to the nearest tenth ? A)0.8B)0.9C)1.7D)5.7 Why was Japan able to colonize Korea, Taiwan and parts of China? The star spangled banner written by frances scott commemorates what event in 1812 : how do network effects help facebook fend off smaller social-networking rivals? What prevented early plants from moving far from water?