A student heated some sulphur in a spatula and collected the gas ' X '. Which one among the following is correct about ' X '?

• A

  X is $\mathrm{SO}_2$ and it turns moist litmus to blue
• B

  X is $\mathrm{SO}_3$ and it turns moist litmus to red
• Correct answer
  C

  X is $\mathrm{SO}_2$ and it turns moist litmus to red
• D

  X is $\mathrm{SO}_3$ and it turns dry litmus to blue

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