Two moles of acetic acid are heated with $P_2O_5$. The product formed is

Oxalic acid when heated with conc. $H_2SO_4$,gives out:

The product $(D)$ in the following reaction sequence is: $HOCH_2CH_2CH_2COOCH_2CH_3$ $\xrightarrow{PCC} (A)$ $\xrightarrow[{(1 \ molar \ equivalent)}]{H_2C=CHMgBr} (B)$ $\xrightarrow{NH_4Cl/H_2O} (C)$ $\xrightarrow[H_2O]{KOH}$ $\xrightarrow{H_3O^{+}}$ $\xrightarrow[pyridine]{(CH_3CO)_2O} (D)$

Dehydration of an organic acid $X$ with concentrated $H_2SO_4$ at $373 \ K$ gives $H_2O$ and gas $Y$. The hybridisation of the carbon in $Y$ and nature of $Y$ are respectively

The strongest acid among the following is

Which of the following is the strongest acid?