In an amino acid,the carboxylic group ionises at $pH = 2.56$ $(pK_{a_1})$ and the ammonium ion ionises at $pH = 9.38$ $(pK_{a_2})$. The isoelectric point of the amino acid is at:

• A
  $11.94$
• B
  $6.82$
• C
  $5.97$
• D
  $3.41$