Question

How many molecules of $C{O}_2$ are present in one litre of air containing $0.03\%$ by volume of $C{O}_2$ at STP?

• A. $8.066\times {10}^{10}$
• B. $8.066\times {10}^{-10}$
• C. $8.066\times {10}^{-18}$
• D. $8.066\times {10}^{18}$

Answer 1

Answer: (D)

$8.066\times {10}^{18}$

At STP, $22.4$ liters of a gas forms one mole that is $6.023\times {10}^{23}$ molecules.

Volume of $C{O}_2$ in $1$ litre of air $=\frac{0.03}{100}\times 1L$

$\therefore$ No. of molecules of $C{O}_2=\frac{6.023\times {10}^{23}}{22.4}\times \frac{0.03}{100}=8.066\times {10}^{18}$