(c) For ‘XNOR’ gate $Y = \overline{A}\ \overline{B} + AB$
$i.e.,\ \overline{0}.\overline{0} + 0.0 = 1.1 + 0.0 = 1 + 0 = 1$
$\overline{0}.\overline{1} + 0.1 = 1.0 + 0.1 = 0 + 0 = 0$
$\overline{1}.\overline{0} + 1.0 = 0.1 + 1.0 = 0 + 0 = 0$
$\overline{1}.\overline{1} + 1.1 = 0.0 = 1.1 = 0 + 1 = 1$