Which of the following compounds will give positive test with Tollen’s reagent?

Which of the following will give yellow precipitate with ${\mathrm{I}}_{\mathrm{2}}/\mathrm{NaOH}$?    

Which of the reagent is used to convert $2-$butanone into propanoic acid?    

$\text{α, β}$-Unsaturated aldehyde is formed in the sequence

Consider the reactions:

$\left(\mathrm{i}\right)$ 

$\left(\mathrm{ii}\right)$ 

Identify $\mathrm{A}, \mathrm{X}, \mathrm{Y}$ and $\mathrm{Z}$.