Which of the following statements about hydrogen is incorrect?

• Correct answer
  A

  Hydrogen has three isotopes of which tritium is the most common.
• B

  Hydrogen never acts as cation in ionic salts.
• C

  Hydronium ion, ${\mathrm{H}}_3{\mathrm{O}}^{+}$ exists freely in solution.
• D

  Dihydrogen acts as a reducing agent

Hence, the correct answer is option: 'A'.