[tex]\Large \boldsymbol {} \sf \displaystyle D(X)_Y = \frac{M(X)}{M(Y)} \\\\\\1.~D(HCl)_{H2} = \frac{36.5}{2} = 18.25\\\\\\2.~D(HBr)_{H2} = \frac{81}{2} = 40.5\\\\\\3.~D(HI)_{H2} = \frac{128}{2} = 64[/tex]