What is the effect of compressed air or nitrogen in the shock strut?

The correct choice highlights that compressed air or nitrogen serves a crucial role in the shock strut by combining with hydraulic fluid for operation. In aircraft landing gear, the shock strut typically consists of a hydraulic cylinder filled with hydraulic fluid and a gas charge, usually nitrogen or compressed air.

The gas charge helps to maintain the hydraulic system's functionality by providing a compressible medium that absorbs the shock during landing. When the landing gear compresses upon touchdown, the hydraulic fluid is forced through orifices, and the gas charge accommodates the volume change, allowing for effective damping of the impact force. This combination is essential for ensuring a smooth landing and maintaining the structural integrity of the aircraft.

The other options do not accurately reflect the primary function of the gas in the shock strut, as they relate to aspects such as noise reduction, weight, or alignment, which are not directly tied to the operational mechanics of the shock absorbing system.