When a mixture of $\mathrm{NaCl},{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ and conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$ is heated in a dry test tube, a red vapor $\left(\mathrm{X}\right)$ is evolved. This vapor $\left(\mathrm{X}\right)$ turns an aqueous solution of $\mathrm{NaOH}$ yellow due to the formation of $\mathrm{Y}. \mathrm{X}$ and $\mathrm{Y},$ respectively, are:

• A

  ${\mathrm{CrCl}}_3$ and ${\mathrm{Na}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$
• B

  ${\mathrm{CrCl}}_3$ and ${\mathrm{Na}}_2{\mathrm{CrO}}_4$
• Correct answer
  C

  ${\mathrm{CrO}}_2{\mathrm{Cl}}_2$ and ${\mathrm{Na}}_2{\mathrm{CrO}}_4$
• D

  ${\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3$ and ${\mathrm{Na}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$

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