Zero hour is a term used in parliamentary procedure to refer to a time period during which members of parliament can raise urgent matters without prior notice. The correct answer, option 2 - Speaker, indicates that the discretion to allow zero hour lies with the Speaker of the Parliament. The Speaker is responsible for maintaining order and upholding parliamentary rules during sessions, and has the authority to determine when zero hour will take place. During zero hour, Members of Parliament can bring up pressing issues that require immediate attention or discussion. This allows for flexibility and responsiveness in addressing urgent matters that may arise during the parliamentary session.