What is the atomic number of a neutral atom which has 51 neutrons and 40 electrons?

A.     40

B.     51

C.     91

D.     131

A

Though this did not affect the correct answer, this question wrongly gave the number of neutrons, rather than the mass number, as 91. The lack of blank responses, the high difficulty index of 75% (remember the higher the number the more accessible the question) and the discrimination index of 0.40 all indicate that this error did not affect the validity of the question.