What must the designated Flight Attendant verify regarding the lithium-ion containment bag during preflight?

The designated Flight Attendant must verify the presence and sealing of the lithium-ion containment bag during preflight because this is crucial for ensuring the safety of the flight. Lithium-ion batteries, if damaged or malfunctioning, can pose significant fire hazards. A properly sealed containment bag ensures that if a battery does overheat or ignite, the flames and any potential smoke are contained, minimizing risk to passengers and crew. Ensuring the bag is present confirms that the appropriate safety measures are in place, while checking the sealing verifies that there is no risk of leakage or exposure to hazardous materials. This procedure is part of adherence to safety protocols aimed at preventing in-flight incidents related to battery-powered devices.