L-isomer of tetrose \( X(\mathrm{C_4H_8O_4}) \) gives positive Schiff’s test and has two chiral carbons. On acetylation, ‘X’ yields triacetate. ‘X’ also undergoes following reactions
\(\text{'A'} \xleftarrow{\text{HNO}_3} \text{'X'} \xrightarrow{\text{NaBH}_4} \text{'B' (Chiral compound)}\)
‘X’ is: