State whether the following statements are true or false.
a. `D` and `L` stereoisomers are enantiomers.
b. `D` enantiomer rotates the plane-polarised light to the right and `L` enantiomer to the left.
c. Conversion of an erythro to a threo stereoisomer always occur by inversion at one chiral `C`.
d. A racemate can be distinguished from a meso or a chiral compound by an attempted resolution.
e. Racemisation of an enantiomer can only occure by breaking of at least one bond to the chiral centre.
f. A reaction catalysed by an enzyme always gives an `O.A` product.
g. When an achiral molecule reacts to give achiral molecule, the product is always racemic
h. In chemical reactions, the change from an `S` reactant to an `R` product always signals an inversion of configuraion.
i. An optically inactive substance must be achiral.
j. An achiral compound can have chiral centres.
K. A compound with `S` configuration is the `(-)` enantiomer.

Explanation

a. F: necessarily. This statement is true only for a compound with one chiral `C` but not for more than one `C` atom. For example

b. F: The terms `D` and `L` do not refer to sign of rotation. They refer to the configuration of stereoisomer relative to that of `D` glyceraldehyde.
c. T: Changing the configuration at one of the chiral centres converts one diastereomer to the other.
d. T: Unlike a racemate, meso and chiral compounds cannot be resolved beacuse they do not consist of enantiomers.
e. T: Only by breaking a bond the configuration can be changed. f. F: The product could be meso or achiral.
g. F : If an optically active achiral coreactant, solvent, or catalyst such as enzyme is used, the product is likely to be `O.A`.
h. F: The priority sequence of ligands may change.
i. F: The racemate shows no optical activity.
j.T: For example, meso compound
k. F: Sign of rotation is not related to the configuration.