A pink solution gives a blue organic layer with NH4SCN/amyl alcohol and a yellow precipitate with KNO2 and acetic acid. For the yellow compound K3[Co(NO2)6], the oxidation state of cobalt and the number of unpaired electrons (nitrite is a strong-field ligand in this complex) are

JEE Advanced levelSingle correct optionDifficulty 3 of 3qc104

A pink solution gives a blue organic layer with $NH X_{4} SCN$ /amyl alcohol and a yellow precipitate with $KNO X_{2}$ and acetic acid. For the yellow compound $K X_{3} [Co (NO X_{2}) X_{6}]$ , the oxidation state of cobalt and the number of unpaired electrons (nitrite is a strong-field ligand in this complex) are

The pink solution is

Co X^{2 +}

. Nitrite oxidises it to Co(III); charge balance in

K X_{3} [Co (NO X_{2}) X_{6}]

gives

3 + x - 6 = 0

, so

x = + 3

. Co(III) is

3 d^{6}

; with strong-field

NO X_{2} X^{-}

the configuration is

t_{2 g}^{6}

, so there are no unpaired electrons.