What is the maximum number of electrons present in K, L and M shell?

The correct solution is option C i.e.the maximum no.of e^–present in K, L and M shells are 2,8 and 18 respectively.

The maximum no.of e^– in a shell/orbit, having principal quantum number (n) =2n².

So, K shell whose principal quantum no., n=1, maximum no.of e^–  =2(1)²=2

Similarly, L shell having n=2, maximum no.of e^– =2(2)²=8 &

M shell having n=3, maximum no.of e^–=2(3)²=18.

Hence, the correct answer is choice C.