To determine who becomes the acting Governor:
1. Under Article 160 of the Indian Constitution, if the office of the Governor falls vacant due to death or resignation, the Chief Justice of the High Court of that state acts as Governor until a new appointment is made.
2. The Chief Secretary, Chief Minister, or Speaker do not assume this role.
3. This ensures continuity in governance.
Therefore, the correct answer is (3) Chief Justice of the High Court.