Important Note: This question has been created from extremely limited feedback. The feedback we have received makes no mention of whether the system is a gaseous or chemical oxygen generated system, yet these are the reported answers. Please let us know if you have any further feedback on this question, thank you!

LO 021.13.01.01.03: Describe the following two oxygen systems that can be used to supply oxygen to passengers: fixed system (chemical oxygen generator or gaseous system); portable
LO 021.13.01.01.04: Describe the actuation methods (automatic and manual) and the functioning of a passenger oxygen mask
LO 021.13.01.01.05: Compare chemical oxygen generators to gaseous systems with respect to capacity; flow regulation.

Refer to figure.
The most common type of passenger oxygen system, and the type most are familiar with from flying on commercial jets, is the chemical oxygen generator type. This type of system uses a solid state chemical canister, which when activated, begins generating gaseous oxygen through a chemical reaction. This reaction starts when passengers pull the masks towards them. With this type of system, once started, the flow of oxygen can not be stopped.

Another type of passenger oxygen system is a gaseous one, which supplies gaseous oxygen to the passenger masks through a centralised system. The masks are deployed at "half height" and the flow of oxygen to each individual mask is only started when the passengers pull the mask towards them. Depending on the system, it may be possible to stop the flow of oxygen to the passenger cabin, or to individual masks.

Reviewing each answer option:

You can start or stop the flow of oxygen to individual masks from the passenger oxygen system. → CORRECT - Although absolutely untrue for chemical oxygen generator systems, this may be the case for a gaseous oxygen supply. The question does not specify how oxygen is supplied to the passengers.

You can control the pressure of oxygen delivered to the cockpit crew only. → INCORRECT - Oxygen pressure is not usually controlled for either the cockpit or passenger oxygen system. Relative oxygen concentration can be somewhat controlled for the cockpit system, by switching between NORMAL and 100% settings.

The system allows you to adjust the concentration of oxygen in the passenger cabin. → INCORRECT - It is usually possible to control the oxygen concentration for the pilots' oxygen system, but not usually the case for a passenger oxygen system.

The system enables you to mix oxygen with cabin air for better temperature control. → INCORRECT - The purpose of the emergency passenger oxygen supply is to allow passengers to breath when the cabin pressure becomes critically low. It has nothing to do with temperature control.