The correct increasing order of basic strength for the following compounds is: 

II < I < III

The correct answer is option 4. II < I < III.

The name of the given compounds are :

Let us evaluate the order of basic strength for the compounds based on the correct option provided:

I. Aniline

Aniline is a basic aromatic amine with an amino group (–NH₂) attached to a benzene ring. It can donate a lone pair of electrons to accept a proton, making it a weak base. It has no electron-donating or electron-withdrawing substituents directly attached to the benzene ring.

II. p-Nitroaniline 

p-Nitroaniline has a nitro group (–NO₂) substituted at the para position of the benzene ring relative to the amino group. The nitro group is electron-withdrawing due to its strong -I (inductive) and -M (mesomeric) effects. It decreases the electron density on the amino group, making it less available to donate electrons. Hence, p-nitroaniline is less basic compared to aniline.

III. p-Methylaniline

p-Methylaniline has a methyl group (–CH₃) substituted at the para position of the benzene ring relative to the amino group. The methyl group is electron-donating due to its +I (inductive) effect, which increases the electron density on the amino group. This makes the lone pair of electrons on the amino group more available to donate, increasing its basicity compared to aniline.

Based on the electronic effects of substituents: II < I < III.

Therefore, the correct increasing order of basic strength for the given compounds is: 4. II < I < III.