Radioactive isotopes called can be used to detect some medical problems.
a. beta particles
b. tracers
c. gamma radiation
d. alpha particles

b. tracers

Explanation:

Radioactive isotopes are the chemical substances which consists of elements which exhibit atoms with unstable nuclei. The unstable nuclei when split or decay results in release of energy in the form of radiation in the form of alpha, beta, and gamma rays.

The tracers are the radioactive isotopes which are used to resolve the medical problems. The tracers are introduced in the body of the patients which when split or decays is tracked by the cameras. This process helps in detecting the cause of diseases and disorders.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.