Question

The number of molecules present in $1.12\times {10}^{-7}cc$ of a gas at STP is:

• A. $6.02\times {10}^{23}$
• B. $3.01\times {10}^{12}$
• C. $6.02\times {10}^{12}$
• D. $3.01\times {10}^{23}$

Answer 1

The correct option is B $3.01\times {10}^{12}$

At STP, 22400 ml of a gas is occupied by $6.023\times {10}^{23}$ molecules.
$\therefore 1.12\times {10}^{-7}ml$ is occupied by $\frac{1.12\times {10}^{-7}\times 6.023\times {10}^{23}}{22400}=3.011\times {10}^{12}$ molecules.

Hence, option B is correct.