Question

Which one of the following pairs of gases contains the same number of molecules?
(A) 3 g of hydrogen and 24 g of oxygen
(B) 11g of CO₂ and 11g of Oxygen
(C) 12 g of O3 and 16g of SO₂
(D) 14g of N₂ and 6g of Methane

Answer 1

maybe (A) I think so...
both given are 3 mols of respective elements

Answer 2

The number of molecules in a  gas ( a particular system ) is the number of moles of the particular compound or element ,as 1 mole has 6.023 * 10 to the power 23 molecules (Avogadro's number)

To find the number of moles the formula is

GIVEN WEIGHT / GRAM MOLECULAR WEIGHT  

1. so the given weight for hydrogen is 3 grams and its gram molecular weight is 2 so the number of moles is 3 /2 which is 1.5 moles
2. for oxygen the number of moles is 24 / 16  as 16 is its gram molecular weight  so 24/16 is 1.5 moles

so we can see that the number of moles  or molecules in both 3 g of hydrogen and 24 g of oxygen have  the same number of molecules. so, your answer is the first option