Assertion (A): At the time of making the contract, if the person is incapable of understanding the contract and making a rational judgment, he is said to have a sound mind.
Reasoning (R): Persons with unsound mind includes idiots, lunatics and drunkard.

A is false but R is correct.

Any person who is a major, i.e., above 18 years of age, is competent to enter into a contract and minors are not competent to enter into a contract. The exception to this rule is that, if a minor enters into a contract and the enforcement of such contract is beneficial for the minor then it will not be held to be void. Furthermore, a person should also have a sound mind and should not be disqualified by any law in force. At the time of making the contract, if the person is capable of understanding the contract and making a rational judgment, he is said to have a sound mind.

Persons with unsound mind - (a) Idiots, (b) Lunatics, (c) Drunkards