Question

The density of a liquid (molar mass 70) is 1.2g/mL. If 2 mL of liquid contains 35 drops,the number of molecules of liquid in one drop is :

• A. $\frac{1.2}{35}\times N_A$
• B. $\frac{1}{35}\times N_A$
• C. $\frac{1.2}{{\left(35\right)}^2}\times N_A$
• D. $1.2N_A$

Answer 1

Answer: (C)

$\frac{1.2}{{\left(35\right)}^2}\times N_A$

Given, 35 drops = 2 mL
$\therefore 1drop=\frac{2}{35}mL=\frac{2}{35}\times 1.2g$
$\therefore No.ofmolecules=\frac{N_A\times 2\times 1.2}{35\times 70}$ $=\frac{1.2}{{\left(35\right)}^2}\cdot N_A$