a
(a) Heat developed by the heater \(H = \frac{{{V^2}}}{R}.\frac{t}{J} = \frac{{{{(200)}^2} \times t}}{{20 \times 4.2}}\)

Heat conducted by the glass \(H = \frac{{0.2 \times 1 \times (20 - \theta )t}}{{0.002}}\)

Hence \(\frac{{{{(200)}^2} \times t}}{{20 \times 4.2}} = \frac{{0.2 \times (20 - \theta )t}}{{0.002}}\)\( \Rightarrow \theta = {15.24^o}C\)