Better method for preparation of BeF _ 2 , among the following is

The beryllium fluoride cannot be easily prepared by simple methods. It is known that beryllium oxide dissolves in aqueous hydrofluoric acid with the formation of the fluoride, but on evaporation of the resulting solution some of the combined acid is lost, and the residue is believed to be an oxy fluoride.

Thermal decomposition of $( {NH}_{4}{)}_{2}{BeF}_{4}$, is the best route for the preparation of ${BeF}_{2}$

${\left({NH}_{4}\right)}_{2}{BeF}_{4} ⟶ 2{NH}_{4}F + {BeF}_{2}$