Q30 / 160 · AP EAMCET 2019 (21 Apr Shift 2) · Chemistry

Which of the following complex ions is most stable?

A
${[Co {(H_{2} O)}_{6}]}^{3 +}$
Correct answer
B
${[Co (CN)_{6}]}^{3 -}$
C
${[Co {(C_{2} O_{4})}_{3}]}^{3 -}$
D
${[{CoF}_{6}]}^{3 -}$

Solution

The stability of a complex ion can be decided with effective atomic number rule.

$EAN = Atomic number of metal - O . N . of metal + 2 \times C . N .$

Oxidation number of cobalt in given complex: $X - 6 = - 3 X = + 3$

So, $EAN = 27 - 3 + 2 \times 6 = 36$ . EAN of this complex is equal to the atomic number next noble gas,so it follows EAN rule. So, it is most stable among given complexes.

Hence, the correct answer is option: 'B'.

Which of the following complex ions is most stable?

Solution

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