Assertion: $[NiCl X_{4}] X^{2 -}$ is paramagnetic whereas $[Ni (CN) X_{4}] X^{2 -}$ is diamagnetic. Reason: Both complexes have the same geometry but chloride and cyanide differ in field strength.

ABoth Assertion and Reason are true, and the Reason is the correct explanation of the Assertion
BBoth Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion
CAssertion is true but Reason is false
DAssertion is false but Reason is true

Answer: C

Ni(II) is

d^{8}

. Tetrahedral

[NiCl X_{4}] X^{2 -}

(

e^{4} t_{2}^{4}

) has 2 unpaired electrons, whereas

[Ni (CN) X_{4}] X^{2 -}

is square planar with all electrons paired. The Assertion is true, but the Reason is false because the two complexes have different geometries (tetrahedral and square planar), and that difference is what causes the magnetic difference.

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Assertion: [NiClX4​]X2− is paramagnetic whereas [Ni(CN)X4​]X2− is diamagnetic. Reason: Both complexes have the same geometry but chloride and cyanide differ in field strength.

Answer: C

More questions on Crystal field theory: splitting, CFSE, spectrochemical series

Assertion: $[NiCl X_{4}] X^{2 -}$ is paramagnetic whereas $[Ni (CN) X_{4}] X^{2 -}$ is diamagnetic. Reason: Both complexes have the same geometry but chloride and cyanide differ in field strength.