Question

The maximum number of electrons in a single d subshell is:
A. 2
B.8
C.4
D. 10
E. 6

Answer 1

2 in any orbital, 10 in a d subshell

2 in an s subshell
6 in a p subshell
14 in an f subshell

Answer 2

btw the wording is sorta ambiguous in your q, a single d subshell would be simply called a d subshell - unless they mean in a d orbital.

Answer 3

The answer is D