What does a synchronized reserve relate to in terms of contingency?

A synchronized reserve specifically pertains to the amount of generating capacity that is immediately available to address a contingency, such as the sudden loss of a large generator or a significant drop in supply. This capacity is designed to provide quick response to ensure grid stability and reliability.

In the context of the given options, stating that synchronized reserve relates to 100% of the largest single contingency means that the reserve should be adequate to address the full impact of losing the largest generator in operation. This ensures that if such an event occurs, the system will have enough resources to replace the lost capacity and maintain balance between supply and demand without risking reliability or stability of the power grid.

The other options suggest different ways of assessing reserves, but in the context of synchronized reserve needed for large contingencies, utilizing 100% of the largest single contingency allows for a comprehensive safeguard against significant disruptions.