Transition metals are known to make interstitial compounds. Formation of interstitial compounds makes the transition metal

Assertion (A): Zr and Hf are of almost similar atomic radii.

Reason (R): This is due to lanthanoid contraction.

Which property of transition metals enables them to behave as catalysts?

Attempt any five of the following:

(a) $\mathrm{Ce}(\mathrm{III})$ is easily oxidised to $\mathrm{Ce}(\mathrm{IV})$. Comment.

(b) $\mathrm{E}^{\circ}\left(\mathrm{Mn}^{2+} / \mathrm{Mn}\right)$ is -1.18 V . Why is this value highly negative in comparison to neighbouring $d$ block elements?

(c) Which element of $3 d$ series has lowest enthalpy of atomisation and why?

(d) What happens when sodium chromate is acidified?

(e) $\mathrm{Zn}, \mathrm{Cd}$ and Hg are soft metals. Why?

(f) Why is permanganate titration not carried out in the presence of HCl ?

(g) The lower oxides of transition metals are basic whereas the highest are amphoteric/acidic. Give reason.

(a) Why is chemistry of actinoids complicated as compared to lanthanoids?

(b) Complete the following reaction and justify that it is a disproportionation reaction:

$$3 \mathrm{MnO}_4^{2-}+4 \mathrm{H}^{+} \rightarrow$$________ $$+$$ _________ $$+$$ $$\mathrm{H}_2 \mathrm{O}$$.

(c) The given graph shows the trends in melting points of transition metals:

Explain the reason why $$\mathrm{Cr}$$ has highest melting point and manganese $$(\mathrm{Mn})$$ a lower melting point.