Correct statements among the following are

A) All optical isomers are optically active

B) Diastereomers are always optical isomers

C) Organic compounds not containing chiral carbon cannot show optical isomersim

D) A compound with an absolute configuration of ‘R’ can be dextro (or) laevo rotatory

A) Meso compound is an optical isomer which is optically inactive

$\therefore$ (A) is false

B) Any two stereo isomers which are not enantiomers are diastereomers. 

Ex:- (i) geometrical isomers are diastereomers (ii) ‘d’ isomer and meso isomer are diastereomers to each other 

$\therefore$ (B) is false

C) Criteria for optical activity is absence of elements of symmetry (disymmetry) but not the presence of chiral carbon alone.

Ex:- CHCl=C=CHCl is optically active but does not contain chiral carbon.

 $\therefore$ (C) is false

D) R(+) and R(-) are possible

 $\therefore$ (D) is true