Final answer:
All of the given statements about radioactive isotopes are correct; they emit radiation upon decay, each has a specific half-life, and the decay rate is constant and characteristic.
Step-by-step explanation:
The correct answer to the question is: d. All of the above are correct. Each radioactive isotope does indeed emit radiation as it decays and has its own specific half-life which is characteristic of that isotope. The decay rate of a radioactive isotope is constant and does not change under different conditions, making it an unchangeable and characteristic rate. These properties are crucial when it comes to practical applications of radioactive isotopes in fields such as medical diagnosis, dating of archaeological finds, and nuclear power.