Electronegativity of carbon atom, also depends on the hybridisation of the carbon atom. Since, $s$-electrons are more strongly attracted by the nucleus than $p$-electrons, thus, electronegativity increases with increase in s-character of the hybridised orbital i.e.,

Thus, $s p$-hybridised carbon is the most electronegative carbon.

Carbon (2.5) is more electronegative than magnesium (1.2) therefore, Mg acquires a partial positive charge while carbon attached to it acquires a partial negative charge.

$\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2-\stackrel{-\delta}{\mathrm{C}} \mathrm{H}_2 \leftarrow \stackrel{+\delta}{\mathrm{Mg}}-\mathrm{X}$

The two isomers which differ in the position of the functional group on the carbon skeleton are called position isomers and this phenomenon as position isomerism. Thus, (A) and (B) may be regarded as position isomers and further they cannot be regarded as metamers since metamers are those isomers which have different number of carbon atoms on either side of the functional group. But here, the number of carbon atoms on either side of sulphur atom (functional group) is the same, i.e., 1 and 3.

Among the following given compounds, according to IUPAC, the longest carbon chain having maximum number of functional group is being selected.

Thus, carbon-chain containing 4 -carbon atoms and which also includes both functional group will be selected. While the other three C-chains are incorrect since none of them contains both the functional groups.

DNA and RNA have nitrogen in the heterocyclic rings. Nitrogen present in rings, azo and nitro groups cannot be converted into $\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4$. That's why Kjeldahl method cannot be used for the estimation of nitrogen present in DNA and RNA.