Question

At $0^{o}C$, 760 mm pressure, the number of molecules present in 3.5 grams of CO gas is:

• A. $6\times {10}^{22}$
• B. $3\times {10}^{22}$
• C. $1.5\times {10}^{22}$
• D. $7.5\times {10}^{22}$

Answer 1

The correct option is D $7.5\times {10}^{22}$

3.5 gram of CO contain $\frac{3.5}{28}=0.125$ moles of CO

We know 1 mole of any gas contains $6.023\times {10}^{23}$ molecules at STP

Number of molecules in 0.125 mole of CO = $6.023\times {10}^{23}\times 0.125=7.5\times {10}^{22}$

Hence, option $D$ is correct.