A failure is an event in which a component or system does not perform a required function within specified limits1. A requirement is a condition or capability needed by a user to solve a problem or achieve an objective2. In this case, the requirement is that the diagnostics tests should execute in less than 2 seconds.
Therefore, any event that violates this requirement is a failure. The only option that clearly violates this requirement is B. The diagnostic tests take too much time to execute. If the diagnostic tests take more than 2 seconds to complete, then they do not meet the specified limit and thus fail. The other options are not necessarily failures related to the specified requirement. Option A. The diagnostic tests fail to start after a system reset is a failure, but not related to the time limit. It is related to the functionality of the self-diagnostics module. Option C. The diagnostic tests that measure the speed of the memory, fail is also a failure, but not related to the time limit. It is related to the accuracy of the memory tests. Option D. The diagnostic tests fail due to incorrect implementation of the test code is also a failure, but not related to the time limit. It is related to the quality of the test code. References = ISTQB Certified Tester Foundation Level Syllabus v4.0, Requirements Engineering Fundamentals.