(a) Show that the number of electron states in a subshell is $4 \ell+2 .$ [Hint: First, how many states are in each orbital? Second, how many orbitals are in each subshell?] (b) By summing the number of states in each of the subshells, show that the number of states in a shell is $2 n^{2}$. [Hint: Use the following theorem: the sum of the first $n$ odd integers, from 1 to $2 n-1$, is $n^{2} .$ That comes from regrouping the sum in pairs, starting by adding the largest to the smallest: