Which out of the following substituent increases the acid strength of phenol.
- CN or -`NH_(2)`

Explanation

To determine which substituent increases the acid strength of phenol between -CN (cyanide) and -NH2 (amino), we can follow these steps:

### Step 1: Understand the Structure of Phenol
Phenol is a benzene ring with a hydroxyl (-OH) group attached. The acidity of phenol is influenced by substituents attached to the benzene ring.

### Step 2: Identify the Effects of Substituents
- **-CN (Cyanide)**: This group is an electron-withdrawing group due to its -I (inductive) and -R (resonance) effects. It pulls electron density away from the benzene ring and the -OH group.
- **-NH2 (Amino)**: This group is an electron-donating group because it has a lone pair of electrons that can be donated to the benzene ring through resonance (+R effect). However, it also has a -I effect, but it is weaker compared to its +R effect.
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