Match the octahedral complex in Column I with its d-electron arrangement in Column II (cyanide is strong field and water is weak field). Column I: P $[Cr (H X_{2} O) X_{6}] X^{3 +}$ ; Q $[Fe (H X_{2} O) X_{6}] X^{3 +}$ ; R $[Co (CN) X_{6}] X^{3 -}$ ; S $[Ni (H X_{2} O) X_{6}] X^{2 +}$ . Column II: 1) $t_{2 g}^{6} e_{g}^{0}$ ; 2) $t_{2 g}^{3} e_{g}^{0}$ ; 3) $t_{2 g}^{3} e_{g}^{2}$ ; 4) $t_{2 g}^{6} e_{g}^{2}$ .

Answer: A

Cr(III) is

d^{3}

t_{2 g}^{3}

. Fe(III) is

d^{5}

high spin:

t_{2 g}^{3} e_{g}^{2}

. Co(III) is

d^{6}

low spin:

t_{2 g}^{6}

. Ni(II) is

d^{8}

t_{2 g}^{6} e_{g}^{2}

. So P-2, Q-3, R-1, S-4.