$\begin{array}{1 1}(a)\;\text{t-BuF in acidic solution >t-BuF in basic solution}\\
(b)\;\text{t-BuCl>2-chloro 2,3,3 trimethyl butane}\\
(c)\;\text{t-BuCl >2-chloro 1,1,1 trifluro 2-methyl propane}\\
(d)\;\text{t-BuCl in 90% }H_2O\text{-10% dioxane>t-BuCl in 90% }D_2O\text{-10% dioxane }\end{array}$
