Question

The number of molecules present in $2.8\,g$ of nitrogen is

• A. $6.023\times10^{22}$
• B. $6.023\times10^{21}$
• C. $6.023\times10^{20}$
• D. $6.023\times10^{23}$

Hint:

Always convert grams into moles first and then multiply by Avogadro's number.

Answer 1

The Correct Option is A

Concept: One mole of any substance contains Avogadro's number of molecules: \[ N_A=6.023\times10^{23} \] For nitrogen gas, \[ \mathrm{N_2} \] Molar mass \[ =28\,g/mol \]

Step 1: Calculate number of moles. Given mass \[ m=2.8\,g \] \[ n=\frac{m}{M} \] \[ n=\frac{2.8}{28} \] \[ n=0.1 \]

Step 2: Calculate number of molecules. \[ \text{Number of molecules} =nN_A \] \[ =0.1\times6.023\times10^{23} \] \[ =6.023\times10^{22} \]

Step 3: Match with the options. Hence option (A) is correct. center minipage0.4

Number of molecules = $6.023\times10^{22}$ minipage center