Merger:
Merger is a legal concept that occurs when two or more separate entities combine to form a single entity. In the context of contracts, merger refers to the situation where two or more contracts are combined or merged into a single contract.

Explanation:
In the given scenario, A initially holds a house under a lease agreement, which means that A is the lessee and the owner of the house is the lessor. However, A later decides to buy the house and becomes the owner. As a result of this transaction, the lease agreement is discharged by merger.

Reason:
When A purchases the house, the roles of the lessee and the lessor are merged into a single entity, A. A is now both the owner and the occupant of the house, eliminating the need for a separate lease agreement. The ownership of the house itself includes the rights and obligations that were previously governed by the lease agreement.

Effect:
The merger of the lease agreement into the ownership of the house effectively discharges the lease agreement. This means that the lease agreement is no longer valid or enforceable, as it has been replaced by the ownership rights of A. A is now free to use and occupy the house as the owner without any obligations under the lease agreement.

Other Options:
- Rescission: Rescission refers to the cancellation or termination of a contract. However, in this scenario, there is no indication that the contract is being cancelled or terminated.
- Waiver: Waiver refers to the intentional relinquishment of a contractual right. It does not apply in this scenario as there is no indication that A has intentionally given up any rights under the lease agreement.
- Remission: Remission refers to the release or forgiveness of a debt or obligation. It does not apply in this scenario as there is no debt or obligation being released or forgiven.

When an inferior right of a party under a contract merges into a superior right of the same person, inferior right vanishes into the superior right this is known as merger in such a case the obligation created by inferior right is discharged. in the given question is an example of Merger here the lease agreement is the inferior right and ownership of the house is the superior right.Thus the contract becomes discharged by Merger therefore option B will be the correct answer