Geminal diols (compounds with two $-OH$ groups on the same carbon atom) are generally unstable. However,which of the following is stable?

$Ph-CH_2-CN \xrightarrow[(1) EtONa]{(2) CH_3-COCl, (3) H_3O^{\oplus}/\Delta} (P)$; Product $(P)$ of the reaction will be

The best reagent to carry out the following conversion is:
$3$-hydroxyethylcyclopentane-$1$-carbaldehyde $\rightarrow$ $1$-ethyl-$3$-methylcyclopentane (with a hydroxy group on the ethyl side chain).
(Note: The image shows the reduction of an aldehyde group $-CHO$ to a methyl group $-CH_3$ while keeping the secondary alcohol $-CH(OH)CH_3$ intact.)

What is the major product of the following reaction?

Which of the following reactions converts the carbonyl group of aldehydes and ketones to a methylene group on treatment with zinc amalgam and concentrated $HCl$?

Identify the suitable reagent for the reaction given below.
$CH_3-CO-CH_3 \xrightarrow[(ii) H_3O^+]{(i) ?} (CH_3)_3C-OH$