CBSE 2026 · Region 3 · Set 1 · Q25 · 3 marks
Answer the following questions about the complexes\[\left[\mathrm{NiCl}_{4}\right]^{2-} \text { and }\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-} \](i)Write the hybridization involved in each case.(ii)Which of them is the inner orbital complex and which one is the outer orbital complex ?(iii)Compare their magnetic behaviour. [Atomic number : Ni = $\displaystyle 28$](b)Name two coordination compounds which are important in biological systems.(ii)What is meant by chelate effect? Give an example.(iii)Why are low spin tetrahedral complexes rarely formed?
Answer the following questions about the complexes\[\left[\mathrm{NiCl}_{4}\right]^{2-} \text { and }\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-} \]
(i)
Write the hybridization involved in each case.
(ii)
Which of them is the inner orbital complex and which one is the outer orbital complex ?
(iii)
Compare their magnetic behaviour. [Atomic number : Ni = $\displaystyle 28$]
(b)
Name two coordination compounds which are important in biological systems.
(ii)
What is meant by chelate effect? Give an example.
(iii)
Why are low spin tetrahedral complexes rarely formed?
Marking-scheme solution
(i)
sp
$\displaystyle 3$, dsp
(ii)
[NiCl4]
$\displaystyle 2$- : outer orbital complex
[Ni(CN)$\displaystyle 4$]
$\displaystyle 2$- : inner orbital complex
(iii)
[NiCl4]
$\displaystyle 2$- : Paramagnetic
[Ni(CN)$\displaystyle 4$]
$\displaystyle 2$- : Diamagnetic
(i)
Haemoglobin, chlorophyll, vitamin B12 , Carboxypeptidase A,
Carbonic anhydrase
(ii)
Formation of stable complexes by di or polydentate ligand with
single metal atom/ ion.
[Pt(en)2Cl2]
$\displaystyle 2$-/ [Co(en)$\displaystyle 3$]
$\displaystyle 3$-
(iii) Because of low crystal field splitting energy or Δt < P
Coordination CompoundsBonding in Coordination CompoundsApplyshort_answermedium
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CBSE Class 12 Chemistry past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.