Answer:
(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.
