Question

The number of water molecules present in a drop of water (volume = 0.0018 ml) at room temperature is

(a) 6.023 x 10¹⁹

(b) 1.084 x 10¹⁸

(c) 4.84 x 10¹⁷

(d) 6.023 x 10²³

Answer 1

Correct option is (a) 6.023 x 10¹⁹

Mass of a drop of water = 0.0018 g = 0.0001 mole

18 g of water = 1 mole

0.0018 g of water = 0.0001 mole

1 mole of H₂O = 6.023 x 10²³ molecules 

0.0001 mole of H₂O = 6.023 x 10²³ x 0.0001 = 6.023 x 10¹⁹ molecules