d
(d) \(I \propto {A^2} \Rightarrow \frac{{{I_2}}}{{{I_1}}} = {\left({\frac{{{A_2}}}{{{A_1}}}} \right)^2} = \frac{{\pi {r^2} - \frac{{\pi {r^2}}}{4}}}{{\pi {r^2}}} = \frac{3}{4}\)

\( \Rightarrow {I_2} = \frac{3}{4}{I_1}\) and focal length remains unchanged