Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecule. Which of the following are acidic?
(i)
(CH3)2CH−NH2∣CH−COOH
(ii) HOOC−CH2−CH2−NH2∣CH−COOH
(iii) NH2−CH2−CH2−CH2−COOH
(iv) HOOC−CH2−NH2∣CH−COOH