Oxidation is de-electronation whereas reduction is electronation. Oxidants are the substances which oxidise others and reduced themselves. On the other hand reductants are the substances which reduce others and oxidised themselves. The oxidation number of an element in a compound decides its nature to act as oxidant or reductant. Oxidation-reduction occur simultaneously and the overall chemical change is called redox reaction. Redox reactions are of three types: (i) Intermolecular redox reactions, (ii) Autoredox or disproportionation reaction, and (iii) Intramolecular redox reactions.
Which of the following shows auto-redox change:
(I) `2HCHỌ+ NaOH rarr HCOONa +H_2O`
(II) `Cl_2 + H_2O rarr HCI+HCIO `
(III) `2Cu^(+) rarr Cu^(2+) + Cu`
(IV) `Cr+2H_(2)O+3OCl^(-) rarr Cr^(3+) + 3Cl^(-) + 6OH^(-)`

Options

A. I, II, III
B. I, IV
C. II, IV
D. II, III

Answer

A

Explanation

It involves oxidation of one molecule on the cost of other.