Consider the following reaction

The number of pi bonds in product B is 

Consider the above chemical reaction and identify product $\mathrm{A}$

Which of the below reactions produce carboxylic acids?

(a)  $\frac{{\mathrm{MnO}}_2}{{\mathrm{CH}}_3{\mathrm{COCH}}_3}$

(b) $\mathrm{Ph}-{\mathrm{CCl}}_3\frac{\text{ (i) aq.NaOH }}{\text{ (ii) }{\mathrm{H}}_2\mathrm{O}/{\mathrm{H}}^{\oplus }}$

(c) ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Br}{\frac{\left(\mathrm{i}\right)\mathrm{Mg}}{\left(\mathrm{ii}\right){\mathrm{CO}}_2}}_{\left(\mathrm{iii}\right){\mathrm{H}}_2\mathrm{O}/{\mathrm{H}}^{\oplus }}$

(d) ${\mathrm{CH}}_3\mathrm{CH}={\mathrm{CHCH}}_3\frac{{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7/{\mathrm{H}}_2{\mathrm{SO}}_4}{\Delta }$

The compound $\mathrm{X}$ in the following reaction scheme:

 is:

Considering the above chemical reaction, identify the product $\mathrm{X}:$

In the above reaction, the reagent "$A$" is :

The major product of the following reaction is: