Rank the following species in order of decreasing nucleophilicity in a polar protic solvent (most $\to$ least nucleophilic):
$(1) \ CH_3CH_2CH_2O^{-}$,$(2) \ CH_3CH_2CH_2S^{-}$,$(3) \ CH_3CH_2C(=O)O^{-}$

In the given reaction,identify the reagent $A$:
$4-nitro-3-bromobenzenediazonium \ chloride \xrightarrow{A} 1-bromo-3-nitrobenzene$

Given below are two statements:
Statement $I$: Benzenediazonium salt is prepared by the reaction of aniline with nitrous acid at $273-278 \ K$. It decomposes easily in the dry state.
Statement $II$: Insertion of iodine into the benzene ring is difficult and hence iodobenzene is prepared through the reaction of benzenediazonium salt with $KI$. In the light of the above statements,choose the most appropriate answer from the options given below:

$A$ solution of methyl amine:

Which of the following compounds gives an even number of Hoffmann's exhaustive methylation and elimination cycles?

What is the nature of an aqueous solution of methylamine?