(b)
$\Lambda_{eq}^{\infty}\left( NH_{4}\ OH \right) = \Lambda_{eq}^{\infty}\ \left( NH_{4}Cl \right) + \Lambda_{eq}^{\infty}\ (NaOH) - \Lambda_{eq}^{\infty}\ (NaCl)$
= (149.74 + 248.1 – 126.4)
$\ \ \ \ \ \ \ \ \ = \ 271.44\ \mathrm{\Omega}^{- 1}\ {cm}^{2}{eq}^{- 1}$