can you explain why b? why not d?

Which could happen if amino acid X is titrated nith NaOH trom phtet to pHte12? Selected Anser: 8 b. X coild have a charge of +1 at low pH and a charge of 2 at high pit. Mrwer: X could have a pKa value less than 7.0 for a polar H-provp. b. X could have a charge of +1 at low pH and a charge of 2 at high phe X could have a pKa value ereater than 7.0 for a non polar Reroup d. X could have a charge of +2 at lew pll and i charge of 2 at high ph