What is Tollen's reagent?

Match the reactions given in Column-$I$ with the suitable reagents given in Column-$II$.

Column-$I$ (Reactions)	Column-$II$ (Reagents)
$(A).$ Benzophenone $\to$ Diphenylmethane	$(1).$ $LiAlH_4$
$(B).$ Benzaldehyde $\to$ $1-$Phenylethanol	$(2).$ $DiBAL-H$
$(C).$ Cyclohexanone $\to$ Cyclohexanol	$(3).$ $Zn(Hg) / \text{Conc. } HCl$
$(D).$ Phenyl benzoate $\to$ Benzaldehyde	$(4).$ $CH_3MgBr$

Acetone and acetaldehyde can be distinguished by

$A$ compound,containing only carbon,hydrogen,and oxygen,has a molecular weight of $44$. On complete oxidation,it is converted into a compound of molecular weight $60$. The original compound is:

$CH_3-CO-CH_3 + [O] \xrightarrow{SeO_2} P + Se + H_2O$. What is $P$ here?

Identify the symmetrical ketone from the following compounds.