Which of the following reagents is used in the preparation of nitroalkane from haloalkane?

Haloalkanes undergo nucleophilic substitution with nitrite ions ($\text{NO}_2^-$), which are ambident nucleophiles capable of attacking through either oxygen or nitrogen atoms.

Alkali metal nitrites like KNO$_2$ and NaNO$_2$ are predominantly ionic, with oxygen's higher electronegativity making it the preferred nucleophilic site, yielding alkyl nitrites: R–X + KNO$_2$ $\rightarrow$ R–O–N=O + KX.

Silver nitrite (AgNO$_2$) is covalent, with the Ag–O bond reducing oxygen's nucleophilicity and favoring nitrogen attack, producing nitroalkanes: R–X + AgNO$_2$ $\rightarrow$ R–NO$_2$ + AgX.

To prepare nitroalkanes from haloalkanes, silver nitrite is the preferred reagent.