A. CH4 or methane which is a chemical compound
To get the number of gold atoms, you have to divide the mass of the gold by the mass of the gold atom. It follows this simple equation

.
Let x be the number of gold atoms. Plug in the values to a calculator.
x =

Both have the same units so the unit gram(g) can be cancelled.
x then would be equal to 1.53x10^22. So there are 1.53x10^22 atoms of gold in 5 g of gold
The answer is B. The chlorine has 7 electrons at the outer shell. So it will gain one electron to become stable when forms a chloride ion. And the gained electron will stay at the outer shell. So the radius becomes larger.
Taking into account the reaction stoichiometry, 2 moles of CaO are required to react with 2 moles of Ca(OH)₂.
<h3>Reaction stoichiometry</h3>
In first place, the balanced reaction is:
CaO + H₂O → Ca(OH)₂
By reaction stoichiometry (that is, the relationship between the amount of reagents and products in a chemical reaction), the following amounts of moles of each compound participate in the reaction:
- CaO: 1 mole
- H₂O: 1 mole
- Ca(OH)₂: 1 mole
<h3>Moles of CaO required</h3>
The following rule of three can be applied: If by stoichiometric reaction 1 mole of Ca(OH)₂ is produced by 1 mole of CaO, 2 moles of Ca(OH)₂ are produced by how many moles of CaO?

moles of CaO= 2 moles
Finally, 2 moles of CaO are required to react with 2 moles of Ca(OH)₂.
Learn more about the reaction stoichiometry:
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