Hydrogen chloride gas, hcl, is an example of an arrhenius acid because

            Hydrogen chloride gas, HCl, is an example of an Arrhenius acid because it produces Hydrogen Ions ( H⁺ ) in water.

Explanation:

                   Acid and Bases are defined according to three different theories and concepts.

                      i) Arrhenius Concept

                      ii) Lowry Bronsted Theory

                      iii) Lewis Theory

According to Arrhenius Concept of Acid and Base, "Acid is any specie which when dissolved in water ionizes to produce H⁺ ions".

Example:

                                  HCl    →    H⁺  +  Cl⁻

                                  H₂SO₄    →    2 H⁺  +  SO₄²⁻

While, "Bases are those species which when dissolved in water produces Hydroxyl Ions (OH⁻)".

Example:

                                  NaOH    →  Na⁺  +  OH⁻

                                  Mg(OH)₂    →     Mg²⁺  +  2 OH⁻

indium, and thallium have three electrons i think