When magnesium and hydrochloric acid react, they produce

The correct option is C

Hydrogen and magnesium chloride

The explanation for the correct option:

(C) Hydrogen and magnesium chloride:

1. Magnesium, being more reactive than hydrogen, displaces it in a chloride molecule, resulting in a single displacement reaction.
2. Magnesium is oxidized when two electrons are lost, and hydrogen is reduced when two electrons are gained.
3. The reaction is as follows $\mathrm{Mg}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{MgCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$.
4. Therefore, magnesium chloride with hydrogen gas is formed.

Explanation for incorrect option(s):

(A) Oxygen and magnesium chloride

No oxygen is formed as there is no oxygen in the reactant also.

(B) Chlorine and magnesium oxide

Magnesium oxide is formed when magnesium is reacted with oxygen.

(D) hydrogen and magnesium oxide

Magnesium oxide cannot be formed because magnesium is reacted with hydrochloric acid.

Hence, the correct answer is an option (C).