Give reasons:
(i) Zirconium (Z = 40) and Hafnium (Z = 72) have almost similar atomic radii.
(ii) d-block elements exhibit more oxidation states than f-block elements.
(iii) The enthalpies of atomization of the transition metals are high
(iv) The variation in oxidation states of transition metals is of different type from that of the non transition metals.
(v) Orange solution of potassium dichromate turns yellow on adding sodium hydroxide to it.

Explanation

(i) Due to lanthonoid contraction, Hf has similar atomic size (158 pm) to that of Zr (160 pm).
(ii) f-block elements show limited number of oxidation states due to large energy gap between outer f, d and s-sub-shells.
(iii) Due to the presence of large number to unpaired electrons in their atoms, they form strong interatomic metallic bonds. Hence, transition metals have high enthalpies of atomization.
(iv) The variability in oxidation states of transition metals is due to incomplete filling of d-orbitals in such a way that their oxidation states differ from each other by unity. e.g.,` Fe^(2+) and Fe^(3+)`. In case of non-transition elements, the oxidation states differ by two units e.g., `Pb^(2+) and Pb^(4+)` and this is due to ns electrons.  
(v) `underset("Orange")(K_2Cr_2O_7) + 2NaOH to underset("Yellow")(K_2CrO_4) + Na_2CrO_4 + H_2O` .