The d and f Block Elements

66.  (i) - (b); (ii)- (a); (iii)- (d); (iv)- (e); (v)- (c)

65.  (i) - (c); (ii)- (d); (iii)- (b); (iv)- (e); (v)- (a)

64. Osmium has the capacity to expands its octet by utilising all the electrons from its 6s and 5d orbitals this results it to attain an oxidation state of +8.

Both the statements assertion and reason are correct but reason is not the correct explanation of assertion. The correct option is B.

63. Cu lies below hydrogen in electrochemical series and has positive electrode potential. hence cannot liberate hydrogen from acids. 

Both the statements assertion and reason are correct and reason is the correct explanation of assertion. 

62. Actinoids are more reactive than lanthanoids as they involve their 5d-orbital in the bond formation process while due to effectively shielded and greater nuclear charge 4f-orbitals are not available for bonding. Thus, lanthanoids comparatively form less complexes than actinoids. 

Assertion is not true but reason is true.

61. Although Zr and Hf lie in same group but As an effect of lanthanide contraction, zirconium and hafnium have similar radius of 160pm and 159 pm respectively. Due to this similarity in their size, they show similar physical and chemical properties. As a result, Zr and Hf are difficult to separate. Both the statements assertion and reason are correct but reason is not the correct explanation of assertion. 

60. All halogens combine with copper to form copper halides except iodine. The reason behind this is that Cu²⁺  oxidises iodide (-1)  to iodine (0). Therefore, Cu²⁺ iodide does not exist .Both the statements assertion and reason are correct and reason is the correct explanation of assertion. 

59.  (B) and (C) 

Electronic configuration of cerium:

Ce  -  4f¹ 5d¹ 6s²

Ce⁴⁺?  4f⁰ 5d⁰ 6s⁰ 

Lead has the tendency to lose its four outer electrons to attain Noble gas configuration and this removal of electrons corresponds to the f? configuration and cause it to be stable in +4 oxidation state

58.  (B) and (C) 

A compound act as oxidising agent when it's central atom is reduced to its lower oxidation state. This occurs only when the lower oxidation state of metal is more stable than the higher oxidation states. 

In metal WO₃ and CrO₄^2- , both W and Cr are stable in their higher oxidation state and won't get reduced to their lower oxidation state. Therefore, will not act as oxidising agents.