Final answer:
Each cycle of the robot's movement nets one step forward, requiring ten cycles to reach the charger ten steps away. Consequently, the robot will take ten steps back in total.
Step-by-step explanation:
The student's question involves a simple arithmetic pattern that can be solved by understanding the displacement of the robot after each sequence of movements. Since the robot moves two steps forward and one step back, each cycle it effectively moves just one step forward towards its charger unit.
Starting at 0, after the first cycle, the robot will be at step 1 (2 steps forward, 1 step back), after the second cycle at step 2, and so on. Because the robot needs to cover a distance of ten steps, it will complete ten such cycles to reach the charger unit.
Therefore, the robot will take one step back at the end of each cycle, resulting in a total of 10 steps back before it reaches the charger. The correct answer to the student's question is (b) 10 steps back.