d
moles of ethane \(=\frac{3 \mathrm{~g}}{30 \mathrm{~g} / \mathrm{mol}}=0.1 \mathrm{~mol} \)

\(\mathrm{C}_2 \mathrm{H}_6+3.5 \mathrm{O}_2 \rightarrow 2 \mathrm{CO}_2+3 \mathrm{H}_2 \mathrm{O}\)

\(1 \mathrm{~mol}\) of ethane gives \(3 \mathrm{~mol}\) of water

\(0.1 \mathrm{~mol}\) ethane gives \(0.3 \mathrm{~mol}\) of water

Number of molecules in \(0.3 \mathrm{~mol}\) water

\(=0.3 \times 6 \times 10^{23}=18 \times 10^{22}\) molecules

value of \(x\) is 18