In a many-electron atom, the total orbital angular momentum (L) and spin (S) are good quantum numbers instead of the individual orbital $\left(\mathrm{I}_{1}, \mathrm{I}_{2}\right)$ and spin $\left(\mathrm{s}_{1}, \mathrm{s}_{2}\right)$ angular momenta in the presence of
(a)inter-electron repulsion
(b)spin-orbit interaction
(c)hyperfine coupling
(d)external magnetic field
Answer
Answer: A ✓ checked by 4AB · confidence high
The source book printed no answer; this one was worked out and checked — see the explanation.
Explanation
Inter-electron repulsion couples the individual l_i and s_i so that only the totals L and S are conserved (Russell–Saunders coupling); spin–orbit coupling then mixes L and S, leaving J good.