Look at the reaction below:

[tex]\[ H_2SO_4(aq) + Mg(s) \longrightarrow MgSO_4(aq) + H_2(g) \][/tex]

Which substance is the acid in the reaction?

A. [tex]\( Mg(s) \)[/tex]
B. [tex]\( H_2(g) \)[/tex]
C. [tex]\( MgSO_4(aq) \)[/tex]
D. [tex]\( H_2SO_4(aq) \)[/tex]



Answer :

To identify the acid in the given reaction, we need to understand the basic definitions of acids. According to the Bronsted-Lowry theory, an acid is a substance that can donate a proton (H[tex]\(^+\)[/tex]).

The reaction given is:
[tex]\[ H_2SO_4(aq) + Mg(s) \longrightarrow MgSO_4(aq) + H_2(g) \][/tex]

Now, let's analyze each substance involved in this reaction:

1. [tex]\[ Mg(s) \][/tex]: Magnesium in its solid form is a metal and not an acid.

2. [tex]\[ H_2(g) \][/tex]: Hydrogen gas is a simple diatomic molecule and does not act as an acid.

3. [tex]\[ MgSO_4(aq) \][/tex]: Magnesium sulfate in aqueous solution is a salt and does not have acidic properties.

4. [tex]\[ H_2SO_4(aq) \][/tex]: Sulfuric acid in aqueous solution is a known strong acid. It can donate protons (H[tex]\(^+\)[/tex]) to other substances in a reaction.

Considering these points, the substance that acts as an acid in the reaction is:

[tex]\[ H_2SO_4(aq) \][/tex]

Therefore, the substance which is an acid in this reaction is [tex]\( H_2SO_4(aq) \)[/tex], which is the fourth option.

Hence, the correct answer is:
[tex]\[ \boxed{4} \][/tex]