(b)
The units of the rate constant for nth order reaction is $\left( \frac{mol}{L} \right)^{1 - n}s^{- 1}$
$\therefore$ for second order reaction,
Unit of rate constant$\left( \frac{mol}{L} \right)^{1 - n}s^{- 1}$
$mol^{- 1}{Ls}^{- 1} = L\ /mol -$s