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)`