What is the maximum number of electrons which can be accommodated in the :

(a) innermost shell of an atom?

(b) outermost shell of an atom?

Number of electrons in a shell = $2n^2$

(a) the innermost shell of an atom is the K shell,

For K shell, n=1

number of electrons = 2

(b) the outermost shell of an atom can accommodate only 8 electrons.

Therefore,

(a) The innermost shell of an atom can accommodate 2 electrons.
(b) The outermost shell of an atom can accommodate 8 electrons.