Question

An acid is:

Answer 1

The best and most correct answer among the choices provided by your question is the third choice or letter C.

An acid is any substance containing a hydrogen molecule.

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Answer 2

Answer: Option (d) is the correct answer.

Explanation:

According to Bronsted-Lowry, acids are the species that can donate a proton whereas bases are the species that can accept a proton.

For example, $NH_{3} + HCl \rightarrow NH^{+}_{4} + Cl^{-}$

Here, HCl is the acid as it is donating a proton to ammonia.

Arrhenius also stated that acids are the substances that dissociate to give hydrogen ions or protons.

Thus, we can conclude that out of the given options an acid is a proton donor.