Question

If $1\text{mL}$ of water contains $20$ drops. Then no. of molecules in a drop of water is
(Given $N_A=6.022\times {10}^{23}$)

• A. $6.023\times {10}^{23}$ molecules
• B. $1.376\times {10}^{26}$ molecules
• C. $1.667\times {10}^{21}$ molecules
• D. $4.346\times {10}^{20}$ molecules

Answer 1

The correct option is C $1.667\times {10}^{21}$ molecules

$1\text{mL}$ of water = $1\text{g}$ of water
$18\text{g}$ of water contains $6.023\times {10}^{23}$ molecules
$1\text{mL}$ of water contains $=\frac{6.022\times {10}^{23}}{18}$ molecules $=20$ drops
$\therefore$ $1$ drop of water will contain $=\frac{6.022\times {10}^{23}}{18\times 20}$
$=1.667\times {10}^{21}$ molecules