In aqueous solution acids loose H+ ions but it exists in aqueous solution as H3O+

Characteristic species of acid in an aqueous solution

Introduction:
When a substance is dissolved in water, it can either act as an acid or a base, depending on its ability to donate or accept protons (H+ ions). In an aqueous solution, the characteristic species of acid is the one that donates protons.

Answer:
The characteristic species of acid in an aqueous solution is H+ (hydrogen ion).

Explanation:

1. Dissociation of acids in water:
When an acid is dissolved in water, it undergoes dissociation, releasing hydrogen ions (H+). For example, when hydrochloric acid (HCl) is dissolved in water, it dissociates as follows:
HCl → H+ + Cl-

2. Formation of hydronium ions:
In aqueous solutions, the hydrogen ions (H+) released by acids do not exist as isolated H+ ions. They quickly react with water molecules to form hydronium ions (H3O+). This reaction can be represented as follows:
H+ + H2O → H3O+

3. Hydronium ions as the characteristic species of acid:
In aqueous solutions, the concentration of hydronium ions (H3O+) determines the acidity. The greater the concentration of hydronium ions, the more acidic the solution. Therefore, in an aqueous solution, it is the hydronium ions (H3O+) that represent the characteristic species of acid.

Comparison with other options:
a) H (hydrogen atom): Hydrogen atoms do not exist as isolated entities in aqueous solutions. They either form covalent bonds with other atoms or react with water to form hydronium ions.
c) H (water molecule): Water molecules can act as both acids and bases. However, in an aqueous solution, the hydronium ions (H3O+) are considered the characteristic species of acid.
d) H4O (tetrahydroxide ion): The H4O ion does not exist in aqueous solutions. It is a hypothetical ion with four hydroxide groups attached to a central hydrogen atom.

Conclusion:
In an aqueous solution, the characteristic species of acid is the hydronium ion (H3O+). This ion is formed when an acid donates a proton (H+) to a water molecule. The concentration of hydronium ions determines the acidity of the solution.