Answer
(a) increase
(b) II
Work Step by Step
(a) We know that when the switch is closed, all the resistors are in parallel. Thus, the effective resistance is reduced and as a result the power dissipated increase because power dissipated is inversely proportional to the resistance at constant voltage; that is, $P=\frac{V^2}{R}$
(b) The best explanation is option (II) -- that is, the equivalent resistance of the circuit is reduced by closing the switch, but the voltage remains the same. Therefore from $P=\frac{V^2}{R}$, we see that the power dissipated increases.
