Which of the following are not acids?

CH₃COOH CO₂ HNO₂ HCOOH CCl₄

Acidity is defined as the proton releasing ability in a solution of a compound. The more is the ability of releasing H⁺, the more it shows acidic character. The main driving force of releasing H⁺ is the stabilisation of the conjugate base.

Among all the compounds given above, CCl₄ is not an acid because it doesn’t have any acidic hydrogen to release or any lone pair to accept electrons.

In the 1^st compound, CH₃COOH is acidic as it produces H⁺ ion in the solution maintaining the equilibrium.

For the CO₂ molecule, it is a Lewis acid which reacts with H₂O to produce carbonic acid in the solution.

For HNO₂ molecule, the compound is acidic as it generates H⁺ in the solution and a NO₂^- ion which is stabilised through resonance.

For HCOOH, it is a strong acid and it generates H+ ion and the conjugate base becomes highly stabilised through resonance.

In case of CCl₄, there is no lone pair to accept H+ or bond to generate H+ in solution. Moreover, the C-Cl bond is more convalent than ionic. So CCl₄ doesn’t show acidity.