Optically inactive compound is

A compound whose molecules are superimposable on their mirror images even through they contain an asymmetric carbon atom is called

Racemic mixture is formed by mixing two

Among the following, the Newmann projections of meso- $2, 3$ -butanediol are

The structural formula of sativene is shown below. How many stereogenic centers  are there in this molecule ?

 $A + B , A$ and $B$ are