The correct order of the thermal stability of hydrogen halides ($\text{H}-\text{X}$) is:

Thermal stability depends on the bond dissociation enthalpy of the $\text{H}-\text{X}$ bond.As we move down the halogen group ($F\to Cl\to Br\to I$):The size of the halogen atom increases.The $\text{H}-\text{X}$ bond length increases.The bond dissociation energy decreases.Therefore, $\text{HF}$ is the most stable and $\text{HI}$ is the least stable.Order: $\text{HF}>\text{HCl}>\text{HBr}>\text{HI}$.