Which piece of emergency equipment is stowed in row 11 OHB A/C on the 65 PAX aircraft?

The correct piece of emergency equipment stowed in row 11 overhead bin A/C on the 65 passenger aircraft is the portable Halon fire extinguisher. This choice is significant because fire safety is a top priority in aviation, and portable Halon fire extinguishers are specifically designed to combat fires that may occur in the aircraft cabin.

Halon extinguishers are favored over water or other types of extinguishers in aviation due to their effectiveness in quickly suppressing flammable liquid and electrical fires without causing collateral damage. The placement of emergency equipment, such as the portable Halon fire extinguisher in a readily accessible location, is crucial for ensuring that the crew can respond promptly in the event of an emergency.

The other options, while they represent important safety equipment as well, do not pertain to the specific location indicated in the question. The first aid kit and emergency medical kit cater to medical emergencies rather than fire incidents, and life vests are stowed in predetermined locations according to the aircraft's safety protocols, usually near exits or in designated storage areas.