Question

Number of water molecules in the drop of water, if $1ml$ of water has $20drops$ and $A$ is Avogadro's number, is

• A. $0.5A/18$
• B. $0\cdot 05A$
• C. $0\cdot 5A$
• D. $0.05A/18$

Answer 1

The correct option is D $0.05A/18$

1 drop of water $=\frac{1}{20}ml=\frac{1}{20}g$

$(d_{H_{2}O}=1g{ml}^{-1})$

$18g$ of water $=A$ molecules

$\therefore \frac{1}{20}g$ water $=\frac{A}{18}\times \frac{1}{20}=\frac{0\cdot 05A}{18}$ molecules

Option D is correct