The number of chiral centres present in threonine is ________.

Consider the following equations :
2Fe²⁺ + H₂O₂ $$ \to $$ xA + yB
(in basic medium)
2MnO₄^- + 6H⁺ + 5H₂O₂ $$ \to $$ x'C + y'D + z'E
(in acidic medium)
The sum of the stoichiometric coefficients x, y, x', y', and z' for products A, B, C, D and E, respectively, is ______.

Which of the following compounds will form the precipitate with aq. AgNO₃ solution most readily?

The major product [R] in the following sequence of reactions as :