Ethanal forms '$\mathrm{x}$' total number of acetals (including stereoisomers) with glycerol. What is the value of '$\mathrm{x}$'?

In which one of the following, all the compounds will give positive Tollen's test?

What is the product $\left(\mathrm{A}\right)$ in the following reaction? 

Which carbonyl group is most reactive for nucleophilic addition reaction ?

End product $\left(\mathrm{B}\right)$ of above reaction