Question

In which one of the following solvents, $HCl$ do not behave as an acid?
(i) Ammonia
(ii) Aqueous $NaOH$
(iii) Benzene
(iv) Water

Answer 1

Try to think in terms of the different types of solvent $($ polar and nonpolar $)$ and their specific characteristics. Also take into account the reaction of an acid and a base $($ neutralization reaction $)$. You will see in polar solvents and in presence of a base $HCl$ will behave as an acid while in non polar solvents the acidity of $HCl$ will be reduced.

Complete step-by-step answer:
Solvents can be of two types Polar Solvent and Non Polar solvent.
Polar solvents are usually composed of compounds in which the atoms have considerable difference in their polarity. So when a compound undergoes ionic dissociation in polar solvents, the ions formed can be stabilized by the oppositely charged ion coming from the solvent. Hence if the solvent is polar and an acid is added, the ${H^ + }$ ion formed is stabilized by the negatively charged ions of the solvent resulting in an increase in acidity $($ since more is the stability of the ${H^ + }$ ion formed, the acid will undergo dissociation to a more extent to form more ${H^ + }$ ions $)$.
While in Non Polar solvents the atoms constituting the solvent do not have considerable difference in their polarity. So when a compound undergoes ionic dissociation in non polar solvents, the ions formed cannot be stabilized by the oppositely charged ion coming from the solvent. Hence if the solvent is non polar and an acid is added, the ${H^ + }$ion formed is not stabilized by the negatively charged ions of the solvent to that extent as in polar solvents resulting in an decrease in acidity $($since less is the stability of the ${H^ + }$ ion formed, the acid will not like to undergo dissociation hence ${H^ + }$ ions formed will be less $)$ .
Also, in the presence of a base an acid undergoes a neutralization reaction quantitatively.
Now, Ammonia $(N{H_3})$is a strong base so in presence of ammonia $HCl$ undergoes a neutralization reaction and hence behaves as an acid.
$NaOH$ is also a strong base so $HCl$ undergoes a neutralization reaction in presence of aqueous $NaOH$ and hence behaves as an acid.
Water $({H_2}O)$ is a polar solvent so the negatively charged $O$ atom present in the water molecule can stabilize the ${H^ + }$ ion obtained from dissociation of $HCl$ molecules hence $HCl$ behaves as an acid in presence of water.
Benzene $({C_6}{H_6})$ is a non polar solvent so it cannot stabilize the ${H^ + }$ ion obtained from the dissociation of $HCl$ molecule hence $HCl$ do not behave as an acid in presence of benzene.

Hence the correct answer is (iii) Benzene.

Note: You must take care whether the solvent given is polar or nonpolar so that you can understand whether the ${H^ + }$ ion formed after dissociation is stabilized or not. Also, you must take into account neutralization reactions for interpreting in which solvent the given molecule does not behave as an acid.