A radioactive isotope, which is used in diagnostic imaging, has a half-life of 6.0 hours. If a quantity of this isotope has an activity of 150 mCi when it is delivered to a hospital, how much activity will remain 24 hours after delivery? (mCi = microcuries)
(A)150 mCi (B)38 mCi (C)19 mCi (D)9.4 mCi
D