C. (2n+1) π/2
I had been asked this question at a job interview.
My question is taken from Trigonometric Functions topic in section Trigonometric Functions of Mathematics – Class 11
The explanation is: We know, cot x is not defined when sin x = 0.
sin x = 0 whenever x is 0, π, 2π, 3π, …. i.e. all integral multiples of π