The correct option is C 37.5 %
If unpolarised light is passed through a polariod P1, its intensity will become half.
So I1=12I0 with vibrations parallel to the axis of P1.
Now this light will pass through second polaroid P2 whose axis is inclined at an angle of 30∘ to the axis of P1 and hence, vibrations of I1. So in accordance with Malus law, the intensity of light emerging from P2 will be
I2=I1cos230∘=(12I0)(√32)2=38I0
I2I0=38=37.5 %