Which stage of cell cycle is called a quiescent stage where the cells are metabolically active without proliferating and with a choice of switching over to a previous phase or stay permanently in it?

The quiescent stage of the cell cycle is called G₀ phase, also known as the resting phase. During G₀ phase, cells are metabolically active, but they are not actively dividing. Instead, they are in a state of arrested growth, where they can remain for an extended period.

In G₀ phase, cells have a choice of either returning to the cell cycle and entering G₁ phase, or staying permanently in G₀ phase.