a
By first polaroid \(P_1\) intensity will be halved then \(P_2\) and \(P_3\) will make intensity \(\cos ^2\left(60^{\circ}\right)\) and \(\cos ^2\left(30^{\circ}\right)\) times respectively.
\(\text { Intensity out }=\frac{256}{2} \times \frac{1}{4} \times\left(\frac{\sqrt{3}}{2}\right)^2=\frac{256 \times 3}{2 \times 4 \times 4}= 2 4\)