how to recognise chiral carbon abd to know optical activity

@ mohit 
a compound can be said as chiral if its non superimposible to its mirror image . 
ex- butan – 2 -ol 
the compound which posses asymmetric carbon are usually chiral , 
i am giving some criteria to identify the chiral carbon 
1- not have plane of symmetry 
2- not have center of symmetry 
FOR carbon to be chiral , it have to be attached to four diffrent group . 
and 1 more thing – carbon forming double covalent bond can never be chiral . 
HOPE IT CLEARS ..