Among the following compounds, which one has the shortest C – Cl bond?

In the following reaction sequence, [C] is :

The number of chiral centres present in threonine is ________.

A 100 mL solution was made by adding 1.43 g of Na₂CO₃.xH₂O. The normality of the solution is 0.1 N. The value of x is _____.

(The atomic mass of Na is 23 g/mol)