In the wet tests for detection of various cations by precipitation, $$\mathrm{Ba}^{2+}$$ cations are detected by obtaining precipitate of

Compound $$\mathrm{A}$$ from the following reaction sequence is:

The total number of stereoisomers for the complex $$\left[\mathrm{Cr}(o x)_{2} \mathrm{ClBr}\right]^{3-}$$ (where $$o x=$$ oxalate) is :

Better method for preparation of $$\mathrm{BeF}_{2}$$, among the following is :