An acid is:

a. a proton acceptor
b. any substance that reacts to keep blue litmus blue
c. any compound containing hydrogen
d. a proton donor
e. a compound having hydrogen as a cation and oxygen as an anion

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,

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.

since electrons are negative the answer is neagtaive