Any question pertaining to the disqualification of a member of the Lok Sabha on the ground of defection is decided by:

Under the Tenth Schedule of the Constitution of India, introduced by the 52nd Amendment Act, 1985, the power to decide on the disqualification of a member of a House on the ground of defection is vested in the presiding officer of that House [2]. For the Lok Sabha, this authority is the Speaker, while for the Rajya Sabha, it is the Chairman [1]. Paragraph 6 of the Tenth Schedule explicitly states that if any question arises regarding such disqualification, it shall be referred to the Speaker or Chairman, whose decision was originally intended to be final [1]. Although the Supreme Court in the Kihoto Hollohan case (1992) ruled that the Speaker's decision is subject to judicial review on grounds of mala fides or perversity, the primary adjudicating authority remains the Speaker. The President's role in disqualification is limited to other grounds under Article 102(1), not defection.

Sources

1. [2] https://ili.ac.in/pdf/10.pdf
2. [1] https://www.mea.gov.in/Images/pdf1/S10.pdf