Answer:
G1
Explanation:
The interphase of the cell cycle has three stages: G1, S, and G2. The G1 phase of the cell cycle is marked by cell growth and replication of cell contents followed by DNA replication in the S phase. DNA replication in the S phase doubles the amount of DNA in the cells. S phase is followed by the G2 phase and then the M phase.
According to the given information, one cell has halted the cell division. The DNA amount in this cell is half as compared to the surrounding dividing cells. This means that the cell has not undergone S phase and DNA has not been replication. The cell division in this cell must have halted at the G1 checkpoint.
The G1 checkpoint checks the cell for its DNA content, nutrients levels, growth factors and other requirements for further stages. If any such requirement is not met, the cell division is halted.