**Q.1 Calculate the number of atoms of carbon present in 25 g of CaCO _{3}.**

**Answer **:

Given,

Wt. of CaCO3 = 25 g

No . of moles of CaCO3 = Wt. given / mol. weight = 25/ 100 = 0.25 mole

(Wt of CaCO3 = 40 + 12 + 48 = 100 )

Again, 1 mole of CaCO3 contains 1 mol of C

0.25 mol of CaCO3 contains 0.25 mol of C

We Know that,

1 mole of C contains 6.022 * 10 ^{23} atoms of C

0.25 mole of C contains 0.25 * 6.022 * 10 ^{23} atoms of C

= 1.5055 * 10 ^{23} atoms of C.