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 :

The major product for the following reaction is:

The naturally occurring amino acid that contains only one basic functional group in its chemical structure is