(a) An element can show 0, -1 and +5 oxidation states . The oxidation number of the elements in two compounds are-1 and +5 is a comproportionation reaction involving these two compounds possible.
(b) Give an example of a compound where the constitument element exhibits fractional oxidation number.

Explanation

(a) In a comproportionation reaction ,two reactants in which a particular element exists in different oxidation sates ,react to form a substance in which that element exists in an intermediate oxidation state . The given oxidation states of the elements in two compounds are -1 and +5 .So, if these two compounds together undergo comproportionation reaction they will form a substance in which the element will exist in the oxidation state of zero. This oxidation state lies between -1 and +5 .Hence the two compounds together can indergo comproportionation reaction . (b) Potassium superoxide (KO_(2)[oxidation state of O- atom =-1/2].