Question

From the following pairs, select the one in which both samples contain same number of atoms:-
1) 2.4g of O2 and 4.2 g of N2
2) 4.4 g of CO2 and 4.6 g of Na
3) 1.4 g of H2SO4 and 560 mL of SO3 (g) at STP
4)6.023*10²³ molecules of H3PO4 and 7.3 g of HCL​

Answer 1

Given info :

1. 2.4g of O2 and 4.2 g of N2
2. 4.4 g of CO2 and 4.6 g of Na
3. 1.4 g of H2SO4 and 560 mL of SO3 (g) at STP
4. 6.023*10²³ molecules of H3PO4 and 7.3 g of HCl

To choose : which both samples contain same number of atoms.

solution : number of atoms = no of moles of molecules  × no of atoms in a molecule × avogadro's number

here avogadro's number is constant. and that is N = 6.023 × 10²³

       option (1) 2.4g of O2 and 4.2 g of N2

number of atoms of O in O2 = 2.4/32 × 2 × N = 0.15N

number of atoms of Nitrogen in N2 = 4.2/28 × 2 × N = 0.3N

it is clear that no of atoms are different.

        option (2) 4.4 g of CO2 and 4.6 g of Na

number of atoms in CO2 = 4.4/44 × 3 × N = 0.3N

no of atoms in Na = 4.6/2 × 1 × N = 0.2N

no of atoms are different in both samples.

        option(3)  1.4 g of H2SO4 and 560 mL of SO3 (g) at STP

no of atoms in H2SO4 = 1.4/98 × 7 × N = 0.1 N

no of atoms in SO3 = 560ml/22400ml × 4 × N = 0.1N

no of atoms are same in both samples.

        option (4) 6.023*10²³ molecules of H3PO4 and 7.3 g of HCl

no of atoms in H3PO4 = (6.023 × 10²³)/6.023 × 10²³ × 8 × N = 8N

no of atoms in HCl = 7.3/36.5 × 2 × N = 0.4N

no of atoms are different in both samples.

therefore the correct option (3)