Meq of $H_2SO_4$ =Meq of NaOH

$N\times 5=84.6\times 2$

$N=\large\frac{84.6\times 2}{5}$

$\;\;\;\;=33.84eq/l$

Weight of $H_2SO_4$ in 1litre =$33.84\times 49$

$\Rightarrow 1.658g/ml$

$\therefore $ purity =$\large\frac{1.658}{1.8}$$\times 100=92.12\%$

Hence (c) is the correct answer.