The dipolemoment of HX is 1.2 D. If the % ionic character of the bond is 25%, then it’s bond length is

% of ionic character  = 

μ_obs = 1.2D
μ_cal = e.d = (4.8x10^-10 esu) (d)
$25=\frac{1.2\times {10}^{-18} \mathrm{esu} \mathrm{cm}}{4.8\times {10}^{-10 }\mathrm{esu}\times \mathrm{d} \mathrm{cm}}\times 100$  

d = 10^-8 cm (or) 10^-10m