Which structure of protein remains intact after coagulation of egg white on boiling?

Identify B formed in the reaction.

$$\mathrm{Cl}-\left(\mathrm{CH}_2\right)_4-\mathrm{Cl} \xrightarrow{\text { excess } \mathrm{NH}_3} \mathrm{~A} \xrightarrow{\mathrm{NaOH}} \mathrm{B}+\mathrm{H}_2 \mathrm{O}+\mathrm{NaCl}$$

Identify from the following species in which $$\mathrm{d}^2 \mathrm{sp}^3$$ hybridization is shown by central atom :

Phenolic group can be identified by a positive: