Question

The gram molecular mass of water is 18 g. The number of water molecules present in 60 g of water is:

• A. $40.10\times {10}^{23}$
• B. $10.02\times {10}^{23}$
• C. $20.05\times {10}^{23}$
• D. $6.68\times {10}^{23}$

Answer 1

The correct option is C

$20.05\times {10}^{23}$

Given mass of water = 60 g
The gram molecular mass of water = 18 g.
Number of moles of water = $\frac{\text{Mass of water}}{\text{Gram molecular mass of water}}$ = $\frac{60}{18}$ = 3.33 mole

1 mole of water contains $6.022\times {10}^{23}$ molecules of water
$\therefore$ The number of water molecules present in 3.33 moles of water
= $3.33\times 6.022\times {10}^{23}$
= $20.05\times {10}^{23}$