Thermodynamically most stable allotrope of phosphorus is:

The reaction of ${\mathrm{P}}_4$ with $\mathrm{X}$ leads selectively to ${\mathrm{P}}_4{\mathrm{O}}_6$. The $\mathrm{X}$ is

Among the following, how many compounds can react with $\mathrm{PC}{\mathrm{l}}_5$ to give $\mathrm{POC}{\text{l}}_3$ ?

 ${\mathrm{O}}_2,\mathrm{C}{\mathrm{O}}_2,\mathrm{S}{\mathrm{O}}_2,{\mathrm{H}}_2\mathrm{O},{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4,{\mathrm{P}}_4{\mathrm{O}}_{10}$