Which of the following is an oxidation-reduction reaction? KOH + HNO3 → H2O + KNO3 CaCl2 + Na2SO4 → CaSO4 + 2NaCl AgNO3 + NaCl → AgCl + NaNO3 Al2(SO4) 3 + 6KOH → 2Al(OH)3 + 3K2SO4 N2 + O2 → 2NO

N2 + O2 → 2NO is an oxidation-reduction reaction.

Explanation:

An oxidation-reduction reaction (also know as Redox reaction) is a type of chemical reaction that involves a transfer of electrons between two species. It occurs when the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron.

We will consider the equations one after the other.

Oxidation numbers of the individual element on the reactant side:

KOH : K = +1, O = -2, H = +1

HNO3 : H = +1, N = +5, O = -2

Oxidation numbers of the individual element on the product side:

H2O: H = +1, O = -2

KNO3: K = +1, N = +5, O = -2

There is no change in the oxidation numbers, hence, it is not an oxidation-reduction reaction.

Oxidation numbers of the individual element on the reactant side:

CaCl2 : Ca = +2, Cl = -1

Na2SO4: Na = +1, S = +6, O = -2

Oxidation numbers of the individual element on the product side:

CaSO4: Ca = +2, S = +6, O = -2

NaCl: Na = +1, Cl = -1

There is no change in the oxidation numbers, hence, it is not an oxidation-reduction reaction.

Oxidation numbers of the individual element on the reactant side:

AgNO3: Ag = +1, N = +5, O = -2

NaCl: Na = +1, Cl = -1

Oxidation numbers of the individual element on the product side:

AgCl: Ag = +1, Cl = -1

NaNO3: Na: +1, N = +5, O = -2

There is no change in the oxidation numbers, hence, it is not an oxidation-reduction reaction.

Oxidation numbers of the individual element on the reactant side:

Al2(SO4)3: Al =+3, S = +6, O = -2

KOH: K = +1, O = -2, H = +1

Oxidation numbers of the individual element on the product side:

Al(OH)3: Al =+3, O = -2, H = +1

K2SO4: K = +1, S = +6, O = -2

There is no change in the oxidation numbers, hence, it is not an oxidation-reduction reaction.

Oxidation numbers of the individual element on the reactant side:

N2: N = 0

O2: O = 0

Oxidation numbers of the individual element on the product side:

NO: N = +2, O = -2

There are changes in the oxidation numbers, hence, it is an oxidation-reduction reaction.