Welcome to your interview.
The question is on your right: Why Volatile Matters in Embedded C. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
Explain what the volatile keyword does in embedded C and why it is needed for hardware-facing or interrupt-shared values. Then give one concrete example where omitting volatile would produce an incorrect program.