Question

At $STP$, volume of a gas in a discharge tube is $1.12\times 10$${}^{-4}$ $ml$. Number of molecules present in the gas are:

• A. $3\times {10}^{23}$
• B. $3\times {10}^{20}$
• C. $3\times {10}^{15}$
• D. $3\times {10}^{19}$

Answer 1

Answer: (C)

$3\times {10}^{15}$

Given :-

At STP volume of gas in a discharge tube = $1.12\times {10}^{-4}ml$

At STP, 22.4 litre volume contains $6.023\times {10}^{23}$ number of molecules.

Therefore, no. of molecules in $1.12\times {10}^{-4}ml=\frac{1.12\times {10}^{-4}ml\times 6.023\times {10}^{23}}{22400ml}=3.015\times {10}^{15}$

Hence, the correct answer is option $\text{C}$.