Question

The noble gas that does NOT occur in the atmosphere is:
A. He
B. Ra
C. Ne
D. Kr

Answer 1

. Generally all noble gasses are present in the atmosphere in minimum concentrations. Argon is the most abundant noble gas with 0.934% and krypton is the noble gas with minimum concentration of 1 ppm in the atmosphere.

Complete step by step answer:
- We have to find which element is not present in the atmosphere among the given options.
- Group VIII A elements are called Noble gases or inert gases.
- Noble gases won’t react with other atoms or molecules that are why they are called as inert gases.
- Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) and Radon (Rn) are the noble gases present in Group VIII A.

- Coming to the given options, option A, Helium. Helium is present in the atmosphere at 5.24 ppm concentration. Then option A is wrong.

- Coming to option C, Neon. Neon is present in the atmosphere at 18.2 ppm in concentration. So, option C is also wrong.

- Coming to option D, Krypton. Krypton is present in the atmosphere at 0.087 ppm in concentration. So, option D is also wrong.

- Coming to option B, Radium (Ra). First of all radium is not a noble gas and it is not available in nature. So, option b is correct.
- Therefore Radium is not a noble gas and it is not present in the atmosphere.
So, the correct answer is “Option B”.

Note: Radium is not available in nature because it is prepared from a radioactive decay of other radioactive elements. The atomic number of radium is 226. Therefore radium is an artificial element which is present in the periodic table.