(A) increases if the average refractive index increases, because if μ is the average refractive index, then angular dispersion is given by the formula ẟ= (μ-1) A. So, if μ increases, (μ-1) will also increase, hence option(A) is correct.

(B) If μ decreases, then (μ-1) also decrease due to which angular dispersion will decrease. So, option (B) is incorrect.

(C) angular dispersion changes with the changing value of refractive index. So, option (C) is incorrect.

(D) Angular dispersion is related to average refractive index by the following formula ẟ= (μ-1) A.

So, option (D) is incorrect.