Question

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

• A. $\frac{1.2\times N_A}{3.5}$
  
• B. $\frac{1.2\times N_A}{35}$
  
• C. $\frac{1.2\times N_A}{(35{)}^2}$
• D. $1.2N_A$

Answer 1

The correct option is C $\frac{1.2\times N_A}{(35{)}^2}$

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