For the given compound X, the total number of optically active stereoisomers is____. The wavy line in the structure means that the stereochemistry at the chiral carbon is unknown.

Stereochemistry at three chiral position is known and other position of stereocenter is unknown , shown in wavy line. We can see that at the double bond and OH we have wavy line. Hence two positions stereochemistry not known then, we can get 8 isomer. of which the below one is optically inactive. Hence the answer is 7.