d
Moles of benzene sulphonic acid before reaction \(II =0.6\,n\)

Moles obtained for phenol (with \(\%\) yield \(=50 \%\) ) = \(0.6 \times 0.5\,n=0.3\,n\)

So over all \(\%\) yield of complete reaction \(=\frac{0.3\,n }{ n } \times 100=30\)