${CuI}_{2}$ is unstable even at ordinary temperature because:

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the ${Cu}^{2 +}$ with a comparatively small radius has a strong polarising power

both (a) and (c)

the $I^{-}$ ion with a large radius has a high polarisability

the ${Cu}^{2 +}$ ion with a 17 electron outer shell has weak polarising power

answer is D.

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Detailed Solution

Because $I^{-}$ is a big ion and the ${Cu}^{2 +}$ ion has a short radius and significant polarizing power, ${CuI}_{2}$ is unstable at ambient temperature. Steric impediment is caused by its wide radius and high polarisability.
Hence, the option D is correct.

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