Using the formula for shell capacity, what is the maximum number of electrons the M shell (n = 3) can hold?

1. Shell capacity is given by $2n^2$. 2. For the M shell, $n = 3$. 3. Capacity $= 2 \times 3^2 = 2 \times 9 = 18$. 4. Rule out A (8 is the L shell) and C (2 is the K shell). _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 2 "Periodic Classification of Elements", p.33_