Question

The number of atoms in 20g of $S{O}_3$ is approximately?

• A. $1\times {10}^{23}$
• B. $1.5\times {10}^{23}$
• C. $2\times {10}^{23}$
• D. $6\times {10}^{23}$

Answer 1

Answer: (D)

$6\times {10}^{23}$

(i) Number of moles $\left(n\right)=\frac{\text{mass of}S{O}_3}{\text{molar mass of}S{O}_3}=\frac{20g}{80gmo{l}^{-1}}=0.25mol$

(ii) Number of molecules of $S{O}_3=$ number of moles $\times$ Avogadro number

$=0.25\times 6.023\times {10}^{23}$

$=1.5\times {10}^{23}$

(iii) $S{O}_3$ is tetra-atomic. Hence, number of atoms present in $20g$ of $S{O}_3=1.5\times {10}^{23}\times 4=6\times {10}^{23}$ atoms