Identify $A$ in the following reaction:

$X \underset{\text{Reductive}}{\stackrel{\text{Ozonolysis}}{\longrightarrow}} Y + Z$. $Y$ can be obtained by Etard's reaction,$Z$ undergoes disproportionation reaction with concentrated alkali. $X$ could be:

The compound which does not respond to iodoform test is

Compound $(A)$,$C_6H_{12}O_3$,when treated with $I_2$ in aqueous sodium hydroxide gives a yellow precipitate. When $(A)$ is treated with Tollens' reagent,no reaction occurs. When $(A)$ is hydrolysed and then treated with Tollens' reagent,a silver mirror is formed in the test tube. Compound $(A)$ will be

Which of the following compounds is most reactive towards nucleophilic attack on the carbonyl group?

After completion of the reactions $(I)$ and $(II)$,the organic compound$(s)$ in the reaction mixtures is (are):