Which of the following statements is not true :

Iodide is the most powerful reducing halide ion, since $I^-$ is the largest and loses its electron most easily (and $I_2$ is the weakest oxidant); true.
Fluorine, the most electronegative element with no d orbitals, shows only the –1 state; true.
In the hypohalous acids HOX, a more electronegative X pulls electron density from the O–H bond, so HOCl ($K_a \approx 3 \times 10^{-8}$) is stronger than HOBr; true.
Among hydrogen halides, acid strength increases HF $\lt$ HCl $\lt$ HBr $\lt$ HI, because the H–X bond becomes weaker. The H–F bond is very strong and HF is a weak acid in water, while HCl is a strong acid.
So the statement that is not true is: HF is a stronger acid than HCl.