Impotency is the first ground available under this section 12(1)(a) which was inserted through the amendment of 1976. Impotency is when there is the lack or absence of capacity to consummate a marriage by an act of normal, natural and complete intercourse.

Impotency can be of two types:
Physical or Mental.

When a person is unable to consummate his/her marriage due to physical or structural deformity, is physical impotency. For instance, small vagina, undue size of male organ.

When a person has some psychological or moral abhorrent or repugnance to sexual activity and on account of this a person is unable to consummate his or her marriage. Thus when the person owing to mental psychological model an emotional reasons is unable to consume it the marriage it is known as mental or psychological impotency.

The only exception is if the disease is curable if important see physical or mental is curable the aggrieved person is barred from moving the court

Barrenness and Sterility will not come under the purview of him putting of impotency a person might be barren or in fertile but if he or she can very well consummate marriage he she is not impotent fellow. Impotency is incapacity to have normal proper sexual intercourse. a person might be barren or sterile but he may be capable of having normal sexual intercourse.

Thus he or she is not impotent. Therefore when a woman cannot conceive or a person cannot father a child or when the cases uterus of the woman gets removed , these are not the case impotency because in all cases of person can have normal sexual intercourse.

Proof of Impotency:
No standard proof is required in such cases .Impotency can be proved by the medical examination or by the conduct of the parties after their marriage or it can be established even by the uncorroborated testimony of the petitioner if is it plausible.

When a person refuses to have sexual intercourse, it cannot be said that person is important but if a person constantly refuse to have intercourse and also failed to submit to medical examination and interface of impotency see can be drawn[1]

Major Case Laws:

1. Yuvraj Digvijay Singh v. Yuvrani Pratap Kumar: [2]
   The Supreme Court of India stated that impotence can be both physical and mental and a party is impotent if his or her mental or physical condition makes consummation of marriage a practical impossibility.
    
2. Urmila Devi Vs. Narinder Singh [3]
   An appeal by the wife was directed against the judgment of the learned District Judge, Shimla whereby he has allowed the petition of the husband and annulled the marriage of the parties under Section 12 of the Hindu Marriage Act, 1955.
   
   This case was later appealed in the High Court of Himachal Pradesh, the court decided that ,the husband has proved beyond doubt that the attitude of the wife towards sex is cold and repugnant. Therefore, she is psychologically impotent and the marriage has not been consummated due to this reason,Therefore the court dismissed the appeal by wife.
   
   

References:

1. Rekha Mathur v. Manish Khanna AIR 2015 Del 197, Jayaraj Anthony v.Meera AIR 1967 Mad 242 (Indian divorce Act)
2. (1969) 2 SCC 279; AIR 1970 SC 137
3. AIR 2007 HP19, 2006(2) ShimLC445