Answer :
The gas preferable for charging a gas-charged accumulator is nitrogen, hence the correct option is 4) Nitrogen.
Nitrogen is chosen because it is inert and does not react with materials commonly found within hydraulic systems. As about 78% of the atmosphere is nitrogen, it becomes the major constituent and acts as the solvent in the air, making it commonly available and relatively inexpensive.
Moreover, using nitrogen helps to avoid the risk of oxidation and other reactions that might occur with reactive gases such as oxygen. Other gases like argon can also be used due to its inertness, but nitrogen is generally preferred due to its cost-effectiveness and easy availability.
Gases like carbon monoxide and oxygen are not used in accumulators due to their reactivity, while carbon dioxide could form carbonic acid in the presence of water, leading to corrosion. Therefore, nitrogen is the best choice for this application.
Therefore, the correct option is 4).
