(d)
Since, $A$ and $B$ are independent events.
$\therefore\ P(A \cap B) = P(A).P(B) = \frac{1}{2} \times \frac{1}{3} = \frac{1}{6}$
Now, $P(A \cup B) = P(A) + P(B) - P(A \cap B)$
$= \frac{1}{2} + \frac{1}{3} - \frac{1}{6} = \frac{2}{3}$
$\therefore\ P\left( \overline{A} \cap \overline{B} \right) = 1 - P(A \cup B)$
$= 1 - \frac{2}{3} = \frac{1}{3}$