A sample has $0.0016\ \text{g}$ of a radioactive isotope. After $4.0$ hours, the mass of the radioactive isotope in the sample decreases to $0.00080\ \text{g}$. Calculate the half-life of the radioactive isotope.
- A$2.0$ hours
- B$4.0$ hours
- C$8.0$ hours
- D$16$ hours