How would the number of atoms in a 2.02g sample of hydrogen compare to the number of atoms in a 32.00g sample of oxygen

Number of atoms is equal.

Explanation:

1 mol of anything contains NA particles.

NA is known as Avogadro's number, 6.02×10²³

We determined the moles of each compound. Both molecules are dyatomic,

H₂  → 2.02 g . 1mol / 2.016 g = 1 mol

O₂ →  32 g . 1mol / 32g = 1 mol

Both have the same amount of moles.

In conclussion, the number of atoms is the same in both samples.

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.

it is stable as it is in group 0 which have full outer shells of electrons