In which stage is a diploid nondividing cell most likely found?

A diploid nondividing cell is most likely found in the G0 phase, which is a stage in the cell cycle. G0 represents a resting or quiescent phase where cells exit the cell cycle and do not actively prepare to divide. Cells in G0 can be considered metabolically active but are not undergoing any preparations for mitosis or meiosis.

In contrast, the G1 phase is a preparatory stage where the cell increases in size and synthesizes proteins and organelles in preparation for DNA synthesis, indicating that cells here are gearing up to divide. The G2 phase follows DNA synthesis and is focused on ensuring that the cell is ready for division, with repairs and further growth occurring. The M phase is where actual cell division occurs, either during mitosis or meiosis, thus not serving as a stage for nondividing cells.

Therefore, G0 is the correct answer for identifying a diploid nondividing cell, as it specifically refers to cells that are in a cycle arrest or a long-term quiescent state.