Question

If half-life of a radioactive material is $5$ years, then the percentage of it remained after $25$ years will be
A.$3.125\%$
B.$6.25\%$
C.$1.25\%$
D.$25\%$

Answer 1

We must remember that the radioactive material is a material which is unstable and decay spontaneously to form another type of material by emitting radiation energies in the form of rays or particles. The materials of radioactive are hazardous, it can ionize radioactive chemicals in the body, and this changes the as usual work of cells.

Complete answer:
We have to know that the time interval for the number of disintegrations per second of a radioactive material to decrease by the one-half, or, equivalently, the required time for the one-half of the radioactive sample to decay (change spontaneously into another element by emitting radiations) is called half-life. Half-life symbol is ${t_{1/2}}$ .
The below equation used to determine the after a certain interval time, how much of the original isotope remains is $\dfrac{1}{{{2^n}}}$ (original mass).
Given, $t = 25$ years and ${T_{1/2}} = 5$ years.
Using the $\dfrac{1}{{{2^n}}}$ equation,
$n = \dfrac{t}{{{T_{1/2}}}} = \dfrac{{25}}{5} = 5$
Then the percentage of radioactive material $25$ years$$= \dfrac{1}{{{2^5}}}{\rm X}100$$$ = 3.125% $From the above calculations,$3.125% $is the answer. **So,Option A.$3.125% $ is the correct answer.**

Additional information:
We must remember that when the human body is exposed to high levels of radioactive materials or radioactivity, it can cause dangerous health effects such as skin burns and acute radiation sickness. Radioactive materials also cause cancer and cardiovascular diseases.

Note:
We have to know that the radioactivity was accidentally discovered by a French physicist Henri Becquerel in 1896. Uranium and polonium are radioactive elements, these are important in the use of the generation of electricity. Nuclear weapons are produced by uranium and polonium. To study living organisms, to dragonize and treat diseases, to monitor various steps in industrial processes, to produce energy for heat and electric power and to sterilize medical instruments and food are the important uses of radioactivity.