Question

which alcohol is most acidic in nature and why

Answer 1

In case of alcohols acidic characters depends upon the O-H bond polarity. More the polar bond more acidic will be the respective alcohol. This polarity gets affected by electron donating group. If electron donating group increases polarity decreases.
The number of electron donating groups decreases in order:
Tertiary alcohol > Secondary alcohol > primary alcohol
Primary alcohols has more polar O-H bond than secondary alcohol and secondary alcohol has more polar O-H bond than tertiary alcohol.

 Thus acidic strenght decreases in the following order:
Primary alcohol > secondary alcohol > tertiary alcohol.