Question

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

(a) 6.022 x 10¹⁹

(b) 1.084 x 10¹⁸

(c) 4.84 x 10¹⁷

(d) 6.022 x 10²³

Answer 1

Correct option is (a) 6.022 x 10¹⁹

Answer 2

Correct option is (a) \(6.022 \times 10^{19}\) 

density of water at room temperature = 1g/mL

\(\therefore\) mass of one drop of water \(=0.0018\,mL\times1\,g/mL=0.0018g.\)

\(\therefore\) Number of moles of water molecule \(=\frac{0.0018}{18}=10^{-4}\) mol.

\(\therefore\) Number of water molecules in one drop \(=6.022\times10^{23}\times10^{-4}\) 

\(=6.022\times10^{19}\).