For $\alpha - $amino acids having the structure$R - \mathop {\mathop {CH - }\limits_{|\,\,\,\,\,\,\,\,\,} }\limits_{N{H_2}\,\,} C{O_2}H$ Which of the following statements are true
(a) Water solubility is maximum at a $pH$ when concentrations of anions and cations are equal
(b) They give ninhydrin test
(c) On reacting with nitrous acid give off ${N_2}$