Match each complex in Column I with its number of unpaired electrons in Column II (H2O is weak field, CN- is strong field). Column I: P $[\mathrm{Fe}(\mathrm{H}{}_2\mathrm{O}){}_6]{}^{2+}$; Q $[\mathrm{Fe}(\mathrm{CN}){}_6]{}^{4-}$; R $[\mathrm{Cr}(\mathrm{H}{}_2\mathrm{O}){}_6]{}^{3+}$; S $[\mathrm{Cu}(\mathrm{NH}{}_3){}_4]{}^{2+}$. Column II: 1 zero; 2 one; 3 three; 4 four.

1. AP-4, Q-1, R-3, S-2
2. BP-4, Q-1, R-2, S-3
3. CP-3, Q-1, R-4, S-2
4. DP-4, Q-2, R-3, S-1