NaBH₄ is used in organic chemistry to convert

NaBH₄ is sodium borohydride which is known as a strong reducing agent. It is commonly used reagent in organic to reduce ketones, aldehydes, and acid chloride into corresponding alcohols.

$\begin{array}{ccc}\underset{\left(\mathrm{Aldehyde}\right)}{\mathrm{R}-\mathrm{CHO}}& \stackrel{{\mathrm{NaBH}}_4}{\to }& \underset{\mathrm{Primary} \mathrm{alcohol}}{\mathrm{R}-{\mathrm{CH}}_2-\mathrm{OH}}\\ \underset{\left(\mathrm{Ketone}\right)}{{\mathrm{R}}_2\mathrm{CO}}& \stackrel{{\mathrm{NaBH}}_4}{\to }& \underset{\mathrm{Secondary} \mathrm{alcohol}}{{\mathrm{R}}_2-\mathrm{CH}-\mathrm{OH}}\\ \underset{(\mathrm{Acid} \mathrm{chloride})}{\mathrm{R}-\mathrm{COCl}}& \stackrel{{\mathrm{NaBH}}_4}{\to }& \underset{\mathrm{Primary} \mathrm{alcohol}}{\mathrm{R}-{\mathrm{CH}}_2-\mathrm{OH}}\end{array}$

Conversion present in option (a) is correct because in this option, shows the conversion of alcohol from ketone.