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# Keeping in mind the enthalpy of formation of HF and HCl i.e. -161 kJ and -92 kJ, respectively, which of the following statements do you think is incorrect?

(a) The affinity of fluorine to hydrogen is greater than the affinity of chlorine to hydrogen.
(b) HF is more stable than HCl
(c) HCl is more stable than HF
(d) HF and HCl are endothermic compounds.

Toolbox:
• Compounds for which $\Delta H_f$ is negative is more stable than the compound for which $\Delta H_f$ is positive.
• Exothermic compounds are more stable than endothermic compounds.
• For exothermic compound, more the heat evolved during the formation of a compound from its elements, more stable it is.
Answer: HCl is more stable than HF
Enthalpy of formation of HF and HCl i.e. -161 kJ and -92 kJ, respectively.
As such HF with $\Delta H_f$ = -161 kJ is less stable than HCl with $\Delta H_f$ = -92 kJ which is more positive.