Electrical Power & Heating Effect question from NEET 1998 (AIPMT)

Answer: (c)

1. Heat $H = I^2 R t$, and temperature rise $\Delta T \propto H \propto I^2$.
2. Doubling $I$ makes $\Delta T$ four times: $4 \times 5 = 20^\circ\text{C}$.
3. So the answer is (c) $20^\circ\text{C}$.