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181.
Explain the following facts:
Transition metals form coloured complexes.

Transition metal form coloured complexes, due to the presence of incomplete d-subshell. The electrons can be excited from one energy level to another with in the d-subshell. The energy required to cause such d-d promotions or transition falls within the visible range for all transition elements. When white light falls on an ion or compound, some of its wave lengths are absorbed due to d-d transition and others are reflected. Therefore, colour of the transition metal ion is that of the reflected light.

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182.

Give reasons:
Among transition metals, the highest oxidation state is exhibited in oxoanions of a metal.

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183.

Give reasons:
Ce⁴⁺ is used as an oxidising agent in volumetric analysis.

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184.

Give reasons:
Zn²⁺ salts are white while Cu²⁺ salts are blue.

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185.

Why La, Gd and Lu has low value of 3rd ionisation enthalpies?

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186. Why is cerium a good analytical reagent?

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187. Given below are the electrode potential values, E° for some of the first row of transition elements:
Elements V(23) Cr(24) Mn(25)Fe(26)Co(27)Ni(28) Cu(29)
E°_M²⁺/M(V) –1.18 – 0.91 – 0.44 – 0.28 –0.28 –0.25 +0.34
Explain the irregularities in these values on the basis of electronic structures of atoms.

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