Mahmoud was just told that his father has cancer. mahmoud's first response is that there must be a mistake and he demands that the doctor repeat his tests. which defense mechanism is at work here?

The correct answer is denial.

Denial is a defense mechanism in which an individual refuses to accept or believe something, because doing so would cause them great distress and emotional disturbance. In this instance, Mahmoud does not want to accept that his father has cancer due to which he denies the diagnosis and says that there has been a mistake in his father's diagnostic tests.