Question

Which of the following is/are radioactive elements among the given options?
A.Nitrogen
B.Radium
C.Uranium
D.Hydrogen

Answer 1

Stable molecules like nitrogen and hydrogen which exist as ${{\text{N}}_2}$ and ${{\text{H}}_2}$ respectively do not undergo radioactivity. Only the unstable species radiate in the smaller nuclei. They are mostly present in the seventh period of the periodic table.

Complete step by step answer:
Radioactivity is the emission. Spontaneous emission of radiation from the unstable nucleus is known as radioactivity and the substances which show this property is known as radioactive substances. Radioactive elements are those elements which keep on decay by emitting subatomic particles or energy. It is due to the imbalance in the nucleus of the radioactive elements. Radioactive elements in the modern periodic table are as follow-
All members of s, p, d and f block of period 7.
From period 6; ${\text{Pm}}$ (Promethium) from f block, ${\text{Po}}$ (Polonium), Astatine and Radon from p block.
From period 5 Technetium of d block.
Nitrogen has much higher bond energy due to the presence of triple bind which makes it very stable. It is present in the atmosphere around seventy one percent. Nitrogen exists in diatomic molecules. Hydrogen also exists as a diatomic molecule, which has a complete duplet. Hence they are very stable and do not undergo radioactivity.
All elements can have radioactive isotopes. If enough neutrons are added to an atom, it becomes unstable and decays. A good example of this is tritium, a radioactive isotope of hydrogen naturally present at extremely low level. Uranium does alpha decay and radium decay positrons.

Thus, correct options are B and C.

Note:
Uranium was discovered by Henry Becquerel in 1896. Radium was discovered by M curie and P curie in 1899.