Three equal resistors connected in series across a source of emf together dissipate 9 W of power. What would be the power dissipated if the same resistors are connected in parallel across the same source.

81 W

Power dissipated in series combination is $ P = \frac{V^2}{R_{eq}} = \frac{V^2}{3R} = 9W$

Power dissipated in parallel combination is $ P' = \frac{V^2}{R_{eq}} = \frac{3V^2}{R}= 9\times 9W = 81W$

The correct answer is Option (3) → 81 W