When a replication fork stops midway in a cell, which checkpoint must get activated predominantly?

The correct option is D G2/M
The cell cycle is tightly regulated at a few points in the cell cycle where the cell decides whether to go forward or not. These are called "check points".

There are 3 main checkpoints for cell cycle.
1. Between G1/S phase
2. Between G2/M phase
3. Between Metaphase and Anaphase

The formation of replication fork takes place during S phase. This means that DNA replication has already started. The cell cycle has already crossed the G1/S checkpoint.

It is the G2/M check point that checks if the DNA is damaged and also if the DNA was properly copied or not. Since the replication fork stopped midway, the DNA has not copied properly, which means that the G2/M checkpoint will get activated and prevent the cell cycle from moving ahead.