I was reading a book and it tells that alkene geometrical isomers are achiral. I wanted to know that is it applicable for alkene geometrical isomers? Thanks in advance.
While in general, you should consider chirality and alkene geometry as orthogonal concepts, the statement in your question isn't even true.
Consider the case of 2,3-pentadiene, aka, 1,3-dimethylallene. This compound is chiral. Any change in the geometry of either of the double bonds provides the other enantiomer.