Correct Answer - C

Here, polaroid `A` polarises light.

Intensity of polarised light from `A = (I_(0))/(2)`

According to law of Malus,

Intensity of light emerging from `B`,

`I_(B) = ((I_(0))/(2)) (cos 45^(@))^(2) = (I_(0))/(2)((1)/(sqrt(2)))^(2) = (I_(0))/(4)`