The number of alphabetical capital letters such as A, B, C, D which are not laterally inverted by a plane mirror is __________

The correct option is C 11

The lateral inversion of the letter means the image of the letter formed by the plane mirror. The letters that have symmetry are not laterally inverted and will have same image formed by a plane mirror.

Capital letters shown with correct mark are symmetric and they are not laterally inverted $=11$

Capital letters $(B,C,D,E,F,G,J,K,L,N,P,Q,R,S,Z)$ are not symmetric and they show lateral inversion $=15$

So, option $\left(C\right)$ is correct.