What is Tollen's reagent?

Arrange the following compounds in decreasing order of reactivity towards nucleophilic addition reaction:
$I: HCHO$
$II: CH_3CHO$
$III: CH_3COCH_3$
$IV: PhCOCH_3$

$A$ compound $A$ has the molecular formula $C_2Cl_3OH$. It reduces Fehling's solution and on oxidation,it gives a monocarboxylic acid $B$. Compound $A$ is also obtained by the reaction of ethanol with chlorine. What is $A$?

Oxidation of ketones involves carbon-carbon bond cleavage. Name the products formed on the oxidation of $2,5-$dimethylhexan$-3-$one.

In the given reaction sequence, the percentage of oxygen in compound $(Q)$ is . . . . . . $\%$. (Nearest integer)

Identify the product obtained when a ketone reacts with hydrazine $(NH_2-NH_2)$.