Arrange the following in the increasing order of basicity:
aniline, p-nitroaniline, p-toluidine.

Explanation

To arrange the compounds aniline, p-nitroaniline, and p-toluidine in increasing order of basicity, we need to analyze the structures and the effects of substituents on the nitrogen atom's ability to donate its lone pair of electrons.

### Step-by-Step Solution:

1. **Identify the Structures**:
- **Aniline**: C6H5-NH2 (benzene ring with an amino group).
- **p-Nitroaniline**: C6H4(NO2)-NH2 (benzene ring with an amino group and a nitro group at the para position).
- **p-Toluidine**: C6H4(CH3)-NH2 (benzene ring with an amino group and a methyl group at the para position).
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