(a) Account for the following:

(i) Zr and Hf have almost similar atomic radii.

(ii) Transition metals show variable oxidation states. 

(iii) Cu+ ion is unstable in aqueous solution.

(b) Complete the following equations:

(i) 2 MnO₂ + 4 KOH + O₂--->

(ii) 2 Na₂CrO₄ + 2 H ⁺ -->

From the given data of E⁰ values answer the following Question:

(i) Which is strongest why is  value exceptionally positive?

(ii) Why is value highly negative as compared to other elements?

(iii) Reducing agent  Cr²⁺ or Fe²⁺? Give reason

(b) Why do actinoids show wide range f oxidation states? Write on the similarity between the chemistry of lanthanoids and actinoids.

How are interhalogen compounds formed? What general compositions can be assigned to them?

(a) Give reasons for the following:

(i) Mn³⁺ is a good oxidising agent.

(ii)   Values are not regular for first row transition metals (3d series).

(iii) Although ‘F’ is more electronegative than ‘O’, the highest Mn fluoride is MnF₄, whereas the highest oxide is Mn₂O₇.

(b) Complete the following equations:

(a) Why do transition elements show variable oxidation states?

(i) Name the element showing the maximum number of oxidation states among the first series of transition metals from Sc (Z = 21) to Zn (Z = 30).

(ii) Name the element which shows only +3 oxidation state.

(b) What is lanthanoid contraction? Name an important alloy which contains some of the lanthanoid metals.

Explain each of the following observations:

(i) With the same d-orbital configuration (d⁴), Cr²⁺ is a reducing agent while Mn³⁺ is an oxidising agent.

(ii) Actinoids exhibit a much larger number of oxidation states than the lanthanoids.

(iii) There is hardly any increase in atomic size with increasing atomic number in a series of transition metals.

When chromite ore FeCr₂O₄ is fused with NaOH in presence of air, a yellow-coloured compound (A) is obtained, which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with KCl forms an orange coloured crystalline compound (C).

(i)Write the formulae of the compounds (A), (B) and C.
(ii)Write one use of compound (C).
                                  
                                                OR

Give reasons:
(i)Mn shows the highest oxidation state of +7 with oxygen but with fluorine, it shows the highest oxidation state of +4.
(ii)Transition metals show variable oxidation states.
(iii)Actinoids show irregularities in their electronic configurations.

What is meant by ‘lanthanoid contraction’?