A protein ‘ X ’ with molecular weight of 70, 000u , on...

Amino acids contain amino ($- {NH}_{2}$) and carboxyl ($- COOH$) functional groups. Depending upon the relative position of the amino group with respect to the carboxyl group, the amino acids can be classified as $\alpha, \beta, \gamma, \delta$ and so on. Only $\alpha -$amino acids are obtained on the hydrolysis of proteins.

So, only in option (B) $\alpha$-amino acid given all the other options are not $\alpha$-amino acids.