The reaction of HClO₃ with HCl gives a paramagnetic gas, which upon reaction with O₃ produces

The correct option is Cl₂O₆.

Step 1: Reaction of HClO₃ with HCl

When chloric acid (${\mathrm{HClO}}_3$) reacts with hydrochloric acid ($\mathrm{HCl}$), chlorine dioxide (${\mathrm{ClO}}_2$) and chlorine gas (${\mathrm{Cl}}_2$) are formed along with water:

$2{\mathrm{HClO}}_3+2\mathrm{HCl}\to 2{\mathrm{ClO}}_2+{\mathrm{Cl}}_2+2H_{2}O$

Among the products, chlorine dioxide (${\mathrm{ClO}}_2$) is an odd-electron molecule (containing 19 valence electrons) and is therefore paramagnetic in nature.

Step 2: Reaction of the paramagnetic gas (ClO₂) with Ozone (O₃)

When paramagnetic chlorine dioxide gas (${\mathrm{ClO}}_2$) reacts with ozone ($O_3$), it is oxidized to dichlorine hexoxide (${\mathrm{Cl}}_2{O}_6$):

$2{\mathrm{ClO}}_2+2O_3\to {\mathrm{Cl}}_2{O}_6+2O_2$

Hence, the reaction of the paramagnetic gas with $O_3$ produces Cl₂O₆.