An inorganic Compound $\text{'}\mathrm{X}\text{'}$ on treatment with concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$ produces brown fumes and gives dark brown ring with ${\mathrm{FeSO}}_4$ in presence of concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$. Also Compound $\text{'}\mathrm{X}\text{'}$ gives precipitate $\text{'}\mathrm{Y}\text{'}$, when its solution in dilute $\mathrm{HCl}$ is treated with ${\mathrm{H}}_2\mathrm{S}$ gas. The precipitate $\text{'}\mathrm{Y}\text{'}$ on treatment with concentrated ${\mathrm{HNO}}_3$ followed by excess of ${\mathrm{NH}}_4\mathrm{OH}$ further gives deep blue coloured solution, Compound $\text{'}\mathrm{X}\text{'}$ is:

• A

  $\mathrm{Co}{\left({\mathrm{NO}}_3\right)}_2$
• B

  $\mathrm{Pb}{\left({\mathrm{NO}}_2\right)}_2$
• Correct answer
  C

  $\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2$
• D

  $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2$

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