Amino acids show amphoteric behaviour. Explain why ?

Tyrosine is an $\mathrm{\alpha }$-amino carboxylic acid shown below:

Write the most stable structural formula -
(a) In its cationic form
(b) In its anionic form
(c) In its dianionic form
(d) In its Zwitter ionic form

Complete the following reactions:

(i) 

(ii) 

(iii) 

(iv)  

Allose, given monosacharide is a/an?