Which is the most acidic compound among the following?

Ethanol

The acidic character of alcohol is due to the polar nature of O-H bond. An electron-donating group (EDG) such as -CH₃, -C₂H₅ increases electron density on oxygen leading to a decrease in polarity of the O-H bond. This decreases the acid strength. Therefore, the decreasing order of acidity of alcohol is: 

Primary > Secondary >>Tertiary