A marriage can be declared null and void if certain legal requirements were not met at the time of the marriage. If these legal requirements were not met then the marriage is considered to have never existed in the eyes of the law. This process is called annulment. It is very different from divorce in that while a divorce dissolves a marriage that has existed, a marriage that is annulled never existed at all. Thus unlike divorce, it is retroactive: an annulled marriage is considered never to have existed.
Conditions of the annulment of the marriage are:
a. The marriage has not been consummated ( no sexual relationship has occurred between the husband and wife)
b. It should not have been in the prohibitive relationships (Husband and wife cannot be as brother and sister, like first or second cousin, or through same father and different mother etc., unless accepted by the caste)
c. This marriage should not have happened through fraud or force and without the consent of both the individuals to the marriage.
d. The marriage should not have happened through the concealment of the facts. (like either parties were married before and later divorced, or have a child through previous relationship)
e. The parties of the marriage should not have the contagious disease which cannot be cured within the specified period of 1 year.
f. The parties of marriage should not be impotent or have the disease which can be unable to bear the family.
Proving of Non consummation of marriage is very difficult.So better to file a case for divorce under the ground cruelty .