The correct answer is (d) Radio – Sodium.
Radioactive sodium (Na-24) is a radioisotope of sodium that is used to measure the speed of blood flow in the human body. It is a beta emitter with a half-life of 15 hours. When injected into the bloodstream, Na-24 is quickly taken up by red blood cells. The beta particles emitted by Na-24 are then detected by a gamma camera, which can be used to create a map of the blood flow in the body.
Radioactive phosphorus (P-32) is also used to measure the speed of blood flow, but it is not as commonly used as Na-24. P-32 is a beta emitter with a half-life of 14 days. It is taken up by red blood cells, but it is not as quickly cleared from the body as Na-24. This means that P-32 can be used to measure blood flow over a longer period of time, but it is not as accurate as Na-24 for measuring short-term changes in blood flow.
Radioactive iodine (I-131) is not used to measure the speed of blood flow. It is a gamma emitter with a half-life of 8 days. It is taken up by the thyroid gland, which is located in the neck. I-131 is used to diagnose and treat thyroid disorders.
Radioactive iron (Fe-59) is not used to measure the speed of blood flow. It is a beta emitter with a half-life of 45 days. It is taken up by red blood cells, but it is not as quickly cleared from the body as Na-24. This means that Fe-59 can be used to measure blood flow over a longer period of time, but it is not as accurate as Na-24 for measuring short-term changes in blood flow.