Consider all possible isomeric ketones, including stereoisomers of MW = 100. All these isomers are independently reacted with $\mathrm{N}\mathrm{a}\mathrm{B}{\mathrm{H}}_4$ (NOTE: stereoisomers are also reacted separately). The total number of ketones that give a racemic product(s) is/are

The general formula of isomeric ketone having molecular mass 100 is ${\mathrm{C}}_6{\mathrm{H}}_{12}\mathrm{O} [6\mathrm{x}12 +12\mathrm{x}1 +16]$.

1] Will not give a racemic mixture on reduction with $\mathrm{N}\mathrm{a}\mathrm{B}{\mathrm{H}}_4$. 

this  ketone have chiral center will give diastereoisomer.

2] Will give a racemic mixture on reduction with $\mathrm{N}\mathrm{a}\mathrm{B}{\mathrm{H}}_4$

3] Will give a racemic mixture on reduction with $\mathrm{N}\mathrm{a}\mathrm{B}{\mathrm{H}}_4$

4] Will give a racemic mixture on reduction with $\mathrm{N}\mathrm{a}\mathrm{B}{\mathrm{H}}_4$

5] Will give a racemic mixture on reduction with $\mathrm{N}\mathrm{a}\mathrm{B}{\mathrm{H}}_4$

6] Will give a racemic mixture on reduction with $\mathrm{N}\mathrm{a}\mathrm{B}{\mathrm{H}}_4$