Will mark ! which balanced equation represents an oxidation-reduction reaction? (explain)

(1) ba(no3)2 + na2so4 ==> baso4 + 2nano3

(2) fe(s) + s(s) ==> fes(s)

(3) h3po4 + 3koh==> k3po4 + 3h2o

(4) nh3(g) + hcl(g)==> nh4cl(s)

(2) Fe(s) + S(s) → FeS(s)

Explanation:

The oxidation-reduction reaction contains a reductant and an oxidant (oxidizing agent).An oxidizing agent, or oxidant, gains electrons and is reduced in a chemical reaction. Also known as the electron acceptor, the oxidizing agent is normally in one of its higher possible oxidation states because it will gain electrons and be reduced.A reducing agent (also called a reductant or reducer) is an element (such as calcium) or compound that loses (or "donates") an electron to another chemical species in a redox chemical reaction.The only reaction that include oxidant and reductant:

(2) Fe(s) + S(s) → FeS(s).

Fe is oxidized to Fe²⁺ in (FeS) (loses 2 electrons). "reducing agent".

S is reduced to S²⁻ in (FeS) (gains 2 electrons). "oxidizing agent".

The first reaction: (1) Ba(NO3)2 + Na2SO4 ==> BaSO4 + 2NaNO3

is replacement reaction.

The third reaction: (3) H3PO4 + 3KOH==> K3PO4 + 3H2O

is acid-base reaction.

The fourth reaction: (4) NH3(g) + HCl(g)==> NH4Cl(s)

is synthesis reaction.

The answer is d.potassium