Consider the acidity of the following carboxylic acids:
$(I)$ $PhCOOH$
$(II)$ $o-NO_2C_6H_4COOH$
$(III)$ $p-NO_2C_6H_4COOH$
$(IV)$ $m-NO_2C_6H_4COOH$
Which of the following is the correct order of acidity?

Sodium acetate reacts with acetyl chloride to form

The order of acidity of compounds $I-IV$ is:

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

The major product formed in the following reaction is
$C_6H_5CH=CH_2$ $\xrightarrow[(ii) H_3O^+]{(i) KMnO_4, KOH, \Delta}$ $\xrightarrow{(iii) Br_2/FeBr_3} \text{Product}$

Oxalic acid reacts with concentrated $H_2SO_4$ to give a mixture of two gases. When this mixture is passed through caustic potash,one of the gases is absorbed. What is the product formed by the absorbed gas with caustic potash?