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MCAT Question A Day - 10/24/14 - Answer!

If the position of an electron is known with 100certainty, which of the following cannot be determined for the same electron?

A.  mass
B.  velocity
C.  charge
D.  spin quantum number

B is correct. According to the Heisenberg uncertainty principle, both the position and the momentum mv of an electron cannot be known with absolute certainty at the same time. Since we know the mass of an electron, the uncertainty must lie in the velocity.

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