Question

The weakest base among the following is:
A.Phenylmethanamine
B.N-methylmethanamine
C.Ethanamine
D.Methanamine
E.Benzenamine

Answer 1

Bases are the molecules which give the $OH^-$ ions in the solutions and they react with the corresponding acids to form the salt and water. The bases are further divided into weak and strong bases.

Complete step by step answer:
The bases and the acids function opposite to each other, the main role of an acid is to increase the concentration of the $H^+$ ions in the solution whereas that of the bases is to reduce the concentration of the H+ ions in the solution. The pH of the solution increases with the increase in the basic nature of the solution. The neutralisation reaction is carried out when the acid reacts with the base to form the salt and water.
Phenylmethanamine also known as Benzyl amine is a stronger acid because the lone pair on the nitrogen atom in the benzyl amine is delocalised. Similarly in the N-methylmethanamine , Ethylamine and in the methenamine the delocalisation of the lone pair of the electron takes place due to which the overall electron density on the molecule does not vary much and thus the compound remains strong in nature. Thus they all are the strong bases and the removal of the OH- ions from them is not very easy or they reduce the concentration of the H+ ions in the solution drastically. Benzenamine is the weakest base among the following since the delocalisation of the lone pair of electrons in it is not possible due to which the electron density on the molecule is fairly low and the compound acts as the weak base in the presence of the acid.
Thus option E. is the correct answer.

Note:
The number of the ionisable hydroxide ions ($OH^-$) ions that can be present in the base is known as the acidity of the base and based on these replaceable ions the bases are classified as monobasic, dibasic and tribasic acids.