Which of the following amino acids is achiral?

Which of the following amino acids contains an alcohol functional group?

Which of the following proteins is present in silk?

Which $\alpha$-amino acid can cross-link peptide chains?

$HC\equiv CH$ $\xrightarrow[HgSO_4]{H_2SO_4} (A)$ $\xrightarrow[(1) NH_3 + HCN]{(2) H_3O^{\oplus}} (B);$ The product $(B)$ of the given reaction is:

What is the total number of essential amino acids?