Silicon-31   14 protons, 14 electrons, and 17 neutrons (Periodic Chart)

    14 protons x 1.00728 amu
+  14 electrons x 0.00055 amu
+  17 neutrons x 1.00867 amu
-   30.97536 amu
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0.28165 amu                   The Correct Answer is B.