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.

If a compound decomposes at its boiling point but is steam volatile, water-insoluble and stable at low pressure, steam distillation can be used for its purification. This technique is applied to separate substances which are steam volatile and immiscible with water.