Which element although situated outside the Radioactive series, has radioactive isotope?

Which among the following is a positively charged particle emitted by a radioactive element?

The radioactive element used in heart-pacemakers is

Which one of the following is not radioactive?

Which one of the following elements' isotopes is used in the treatment of cancer?

Which of the following radioactive substances enters the human body through food chain and causes many physiological disorders?