Which reagent is used to distinguish Acetophenone and Benzophenone?

Which one of the following is not formed by aldol condensation of a mixture of ethanal and propanal?

What is the product '$X$' in the following reaction?
(Image of $3-$formylcyclohexanone reacting with $[Ag(NH_3)_2]^+$)

Which of the following compounds gives a positive test with $2,4$-$DNP$ ($2$,$4$-dinitrophenylhydrazine)?
$(a)$ Acetone
$(b)$ Butan-$2$-one
$(c)$ Acetaldehyde
$(d)$ Formaldehyde

An organic compound with the molecular formula $C_9H_{10}O$ forms a $2,4-DNP$ derivative,reduces Tollens' reagent,and undergoes the Cannizzaro reaction. On vigorous oxidation,it gives $1,2-benzenedicarboxylic$ acid. Identify the compound.

The final product of the given reaction is?