**Q.1. How many moles of oxygen molecules are present in 112 mL of O _{2 }gas at NTP?**

we know that,

22400 mL of O_{2} gas contains 1 mole of O_{2}

112 mL of O_{2} gas contains 112/22400 mol of O_{2}

= 0.005 mol of O_{2} gas.

Hence, 0.005 moles of oxygen molecules are present in112 g of O_{2} at NTP.

**Q.2. How many molecules are contained in 0.35 mol of N _{2}?**

we know that,

1 mole of N_{2} will contain 6.002 * 10 ^{23} molecules of N_{2}.

0.35 mole of N2 will contain 0.35 * 6.002 * 10 ^{23} molecules of N_{2} .

= 2.17 * 10 ^{23} molecules of N_{2} .

Hence, there are 2.17 * 10 ^{23} molecules of N_{2} are present in 0.35 mol of N_{2}.

**Q.3. How many moles of atoms are contained in 15 g of Zn?**

we know that ,

mass of Zn is 65.4

now, no of moles of atoms = mass in g/ atomic mass

= 15/65.5 = 0.23 mol.

0.23 moles of atoms is contained in 15 g of Zn.