Q.Discuss five applications of radioactivity for peaceful purpose.

The radioisotope $_{26}Fe^{59}$ (iron-59) is used to diagnose anaemia.

Radioactive iron-59 behaves chemically identically to ordinary iron and is taken up by the body the same way, so it can be used as a tracer to study the rate of formation of red blood cells and the utilisation/absorption of iron in the blood. Monitoring its radioactivity in the blood over time reveals abnormalities in iron metabolism that indicate anaemia. $_{15}P^{31}$ is a stable, non-radioactive isotope; $_{11}Na^{24}$ is used as a tracer to study blood circulation/flow rate; $_{15}P^{32}$ is used in the treatment (and some diagnosis) of certain cancers such as leukaemia — not specifically for diagnosing anaemia.

Phosphorus-32 is the radioisotope classically used as an agricultural tracer, to follow phosphate fertiliser uptake in plants.

Radioisotopes are widely used as 'tracers' in agriculture, medicine, and industry, exploiting the fact that a radioactive isotope of an element behaves chemically identically to its stable counterpart but can be tracked by detecting the radiation it emits, even in extremely small (trace) quantities. In agriculture, one of the most important and long-standing applications is the use of $^{32}_{15}$P (phosphorus-32), a $\beta^-$-emitting isotope with a half-life of about 14.3 days, to study how plants absorb phosphate from fertilisers, how phosphorus moves through the plant (from roots to leaves and other tissues), and how efficiently different fertiliser formulations or application methods deliver phosphorus to crops — since phosphorus is one of the essential macronutrients for plant growth.

Option (a), $^{31}_{15}$P, is simply the ordinary stable (non-radioactive) isotope of phosphorus that makes up virtually all naturally occurring phosphorus — it emits no radiation and so cannot be tracked as a tracer. Options (c) and (d), $^{23}_{11}$Na and $^{24}_{11}$Na, are isotopes of sodium; $^{23}_{11}$Na is the ordinary stable isotope with no radioactivity, while $^{24}_{11}$Na is indeed a radioisotope, but it is characteristically used in medicine (for example, to study blood circulation and locate obstructions in blood vessels) and in industrial leak-detection, not as the standard agricultural tracer — that role belongs specifically to $^{32}_{15}$P.