JEE Main · 2026 · 23 Jan 2026 · Shift 1 · Atomic Structure

For a shell with principal quantum number $n=5$, the azimuthal quantum number may be $l=0,1,2,3,4$. A magnetic quantum number $m_l=-1$ is permitted only when $l\ge 1$, that is for $l=1,2,3,4$, so four orbitals carry an $m_l=-1$ state. Each such orbital holds two electrons of opposite spin, giving a maximum of $4\times 2=8$ electrons with $n=5,m_l=-1$. The set $n=3,l=2,m_l=-1,m_s=+\frac{1}{2}$ fixes every quantum number and so specifies a single spin-orbital, which accommodates exactly one electron. The maximum numbers of electrons for (A) and (B) are 8 and 1 respectively.