Determine which one of the following relations on $X=\{1,2,3,4\}$ is not transitive.

• A

  $R_{1}=\phi$, the empty relation
• B

  $\mathrm{R}_{2}=\mathrm{X} \mathrm{x} \mathrm{X}$, the universal relation
• Correct answer
  C

  $\mathrm{R}_{3}=\{(1,3),(2,1)\}$
• D

  $\mathrm{R}_{4}=\{(1,1),(1,2),(2,3),(1,3),(4,4)\}$

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