In esterification,the $OH^-$ ion for making $H_2O$ comes from

The strongest of the four acids listed below is

Considering the acidity of carboxylic acids:
$(I) PhCOOH$
$(II) o-NO_2C_6H_4COOH$
$(III) p-NO_2C_6H_4COOH$
$(IV) m-NO_2C_6H_4COOH$
What is the correct order of acidic strength?

If there is a compound with the formula $CH_3C(OH)_3$,which one of the following compounds would be obtained from it without reaction with any reagent?

Which one of the following is not an intermediate in the generally accepted mechanism for the reaction shown below?
$CF_3C(O)OH + CH_3CH(OH)CH_3 \xrightarrow{H_2SO_4} CF_3C(O)OCH(CH_3)_2 + H_2O$

When formic acid is heated with conc. $H_{2}SO_{4}$,the gas evolved is