Question

What is the substance that forms Hydronium ion in water (Arrhenius)?
A) Base
B) \[KOH\]
C) Acid
D) None of these

Answer 1

Hint: It is easy to identify a base and an acid. A base usually contains a hydroxide ion $(OH^-)$ and an acid contains \[{H^ + }\] ion. We have to know that an acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. A base is a molecule or ion able to accept a hydrogen ion from an acid.

Complete answer:
Before solving this question we must know what Arrhenius base and acid are?
Arrhenius acid:
On making an aqueous solution of \[HCl\], it dissociates itself into \[{H^ + }\] and \[C{l^ - }\] ions.
\[HCl \to {H^ + } + C{l^ - }\]
As the concentration of \[{H^ + }\] increases in the solution, thus \[HCl\] is an Arrhenius acid.
Arrhenius base:
In water \[KOH\]fully dissociates in water to give \[{K^ + }\] and \[O{H^ - }\] ions.
\[KOH \to {K^ + } + O{H^ - }\]
As the concentration of \[O{H^ - }\](hydroxide ion) increases in the solution, thus \[KOH\] is an Arrhenius base.
So this is a correct option that defines Arrhenius base.
Option A) this is an incorrect option, as a base does not release \[{H^ + }\] instead it increases the concentration of \[O{H^ - }\] ions thus this option is not correct.
Option B) this is an incorrect option, as just now we have discussed that a base does not release \[{H^ + }\] and \[KOH\] is a base.
 Option C) this is a correct option as acid is a substance that forms hydronium ions in water.
According to Arrhenius concept, an acid when dissolved in water releases \[{H^ + }\] since when an Arrhenius acid releases \[{H^ + }\], \[{H_2}O\] molecule accept it forming Hydronium ion(\[{H_3}{O^ + }\])
\[{H_2}O + {H^ + } \to {H_3}{O^ + }\]
Option D) this is an incorrect option .

Option C as the correct answer.

Note:
We have to remember that sometimes, when an Arrhenius base reacts with an Arrhenius acid the products so formed are water and a salt, this type of reaction may be called a Neutralization reaction. Also, Arrhenius theory is limited to acid-base chemistry only.