Better method for preparation of \( \mathrm{BeF}_2 \), among the following is :
\( (\mathrm{NH}_4)_2\mathrm{BeF}_4 \xrightarrow{\Delta} \mathrm{BeF}_2 \)
\( \mathrm{Be} + \mathrm{F}_2 \xrightarrow{\Delta} \mathrm{BeF}_2 \)
\( \mathrm{BeH}_2 + \mathrm{F}_2 \xrightarrow{\Delta} \mathrm{BeF}_2 \)
\( \mathrm{BeO} + \mathrm{C} + \mathrm{F}_2 \xrightarrow{\Delta} \mathrm{BeF}_2 \)