For which of the following van't Hoff factor cannot be greater than unity?

• A

  ${\text{K}}_{\text{4}}\left[\text{Fe}{\left(\text{CN}\right)}_{\text{6}}\right]$
• B

  ${\text{AlCl}}_3$
• Correct answer
  C

  ${\text{NH}}_{\text{2}}{\text{CONH}}_{\text{2}}$
• D

  ${\text{KNO}}_3$

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