Hydrogen fluoride has greater ionic character than hydrogen chloride due to the significantly higher electronegativity of fluorine compared to chlorine, making this relationship a matter of fundamental chemical principles.
The claim is based on the well-established periodicity of electronegativity within the halogens (fluorine being the most electronegative element), making the greater ionic character of HF compared to HCl a fundamental piece of chemical common knowledge based directly on definitions and basic periodic trends.