(a) Why do transition elements show variable oxidation states?
(i) Name the element showing 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.

Explanation

(a) The transition metals have there valence electrons in (n - 1) d and n s orbitals. Since, there is very little energy difference between these orbitals, both energy levels can be used for bond formation. Thus, transition elements exhibit variable oxidation states.
(i) Mangense.
(ii) Boron, aluminium, scandium, gallium, yttrium, indium, Lanthanum, are snows only + 3 oxidation state.
(b) The overall decrease in atomic and ionic ratio from lanthanum to lutetium due to the imperfect shielding of one electron by another in the same subshell is known as lanth anoid contraction.
An important alloy containing lanthanoid metals is much metal which contains 95% lanthanoid metals and 5% iron along with traces of S, C, Ca and Al. It is used in . Mg-based alloy to produce bullets, shells and lighter flints.