Dipole

Electronegativity and therefore dipole moment increases as we move across the periodic table from left to right in a single period. Therefore, for hydrogen halide, ( $\ce{HF}$ , $\ce{HCl}$ , $\ce{HBr}$ , and $\ce{HI}$ ), $\boxed{\ce{HF}}$ has the largest dipole moment. This is confirmed by from the following table of dipole moments of various molecules from this page of General Chemistry.

$\underline {\text{Dipole Moments of Specific Molecules}} \\ \begin{array} {cl} \text{Molecule} & \text{µ (debye)} \\ \hline \\ \ce{H2O} & 1.85 \\ \ce{HF} & 1.91 \\ \ce{HCl} & 1.08 \\ \ce{HBr} & 0.80 \\ \ce{HI} & 0.42 \\ \ce{CO} & 0.12 \\ \ce{CO2} & 0.00 \\ \ce{NH3} & 1.47 \\ \ce{PH3} & 0.58 \\ \ce{AsH3} & 0.20 \\ \ce{CH4} & 0.00 \\ \ce{NaCl} & 9.00 \end{array}$