Complete the following reaction sequence and give the name of major product 'P'.

To determine the major product P, we analyze each step of the reaction sequence starting from propanenitrile $$CH_3CH_2CN$$.

Treatment of a nitrile with aqueous base followed by acidification results in complete hydrolysis of the nitrile group to a carboxylic acid. Thus,

$$CH_3CH_2CN \xrightarrow{OH^-/H_2O,\ \Delta} CH_3CH_2COO^- \xrightarrow{H_3O^+} CH_3CH_2COOH.$$

Therefore, the intermediate formed is propanoic acid.

The next step involves treatment with $$Cl_2$$ and red phosphorus followed by hydrolysis, which is the Hell-Volhard-Zelinsky (HVZ) reaction. This reaction selectively replaces an $$\alpha$$-hydrogen of a carboxylic acid with a chlorine atom. Since propanoic acid contains two $$\alpha$$-hydrogens on the carbon adjacent to the carboxyl group, one of them is substituted by chlorine to give

$$CH_3CH_2COOH \xrightarrow{Cl_2,\ \text{Red P}} CH_3CHClCOOH.$$

Hence, the major product P is 2-chloropropanoic acid with the structure

$$CH_3CHClCOOH.$$

Therefore, the correct answer is 2-chloropropanoic acid, corresponding to option A.