Step 1: Recall what the Tenth Schedule covers.
The Tenth Schedule lays down the anti-defection law that can disqualify a member for switching parties after being elected.
Step 2: Eliminate the wrong deciding authorities.
The Prime Minister, the President, and the Rajya Sabha Chairperson do not decide disqualification questions relating to Lok Sabha membership.
Step 3: Confirm who actually decides.
The Speaker of the Lok Sabha is the presiding officer empowered to decide questions of disqualification for members of that House under the Tenth Schedule.
\[ \boxed{\text{Speaker of the Lok Sabha}} \]