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    Question

    An atom has 7 electrons in its M-shell and contains 18 neutrons in its nucleus. What is its mass number?

    A 35 Correct Answer Incorrect Answer
    B 37 Correct Answer Incorrect Answer
    C 42 Correct Answer Incorrect Answer
    D 25 Correct Answer Incorrect Answer

    Solution

    The atom has 2 electrons in K, 8 electrons in L and 7 electrons in M = 2 + 8 + 7 = 17 and nucleus has 18 neutrons, so its mass number = (number of electrons + neutrons) = 17 + 18 = 35.

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