Question

The density of liquid (mol. wt. = 70) is 1.2 g mL${}^{-1}$. If 2 mL of liquid contains 35 drops, the number of molecules of liquid in one drop is

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

Wt. of one drop of liquid =$\frac{(1.2\times 2)}{35}gram$
70 gram of liquid contain NA molecules
$\frac{(1.2\times 2)}{35}$ gram of liquid contain = $\frac{N_A\times 1.2\times 2}{70\times 35}=\frac{1.2}{(35{)}^2}{N}_A$