Question

chemical group
structure
hydroxyl
(may be written ho—)
in a hydroxyl group (—oh), a hydrogen atom is bonded to an oxygen atom, which in turn is bonded to the carbon skeleton of the organic molecule. (do not confuse this functional group with the hydroxide ion, oh⁻.)
carboxyl
when an oxygen atom is double - bonded to a carbon atom that is also bonded to an —oh group, the entire assembly of atoms is called a carboxyl group (—cooh).
amino
the amino group (—nh₂) consists of a nitrogen atom bonded to two hydrogen atoms and to the carbon skeleton.
make connections given the information in this figure and what you know about the electronegativity of oxygen (see concept 2.3, p. 39), predict which of the following molecules would be the stronger acid (see concept 3.3, p. 53). explain your answer.
which of the functional groups shown above is most likely to gain a proton and become positively charged?
the carboxyl group is most likely to gain a proton.
the hydroxyl group is most likely to gain a proton.
the amino group is most likely to gain a proton.

Explanation:

Amino groups ($-NH_2$) have a lone - pair of electrons on the nitrogen atom. This lone - pair can accept a proton ($H^+$) to form $-NH_3^+$, becoming positively charged. Hydroxyl groups ($-OH$) and carboxyl groups ($-COOH$) are more likely to donate protons rather than accept them in most cases.

Answer:

The amino group is most likely to gain a proton.