Question

The elements with atomic numbers 2, 10, 18, 36, 54 and 86 are all:
A) halogens
B) noble gases
C) noble metals
D) light metals

Answer 1

The atomic mass of the element relates to the nucleus which is present in the centre of the atom. But the properties of the elements depend upon the electronic configuration which is linked with the atomic number. Therefore, atomic number is a better basis for the classification of the elements than the atomic mass.

Complete step by step answer:
We have been provided with elements having atomic numbers 2, 10, 18, 36, 54 and 86,
The atomic number or proton number of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus,
We are supposed to tell under which category does all these elements belong to,
So, if we write the electronic configuration of all these elements:
$\begin{aligned} & 2=2 \\\ & 10=2,8 \\\ & 18=2,8,8 \\\ & 36=2,8,8,18 \\\ & 54=2,8,8,18,18 \\\ \end{aligned}$
We could find that all these elements are stable and have completely filled shells,
The noble gases make up a class of chemical elements with similar properties; under standard conditions, they are all odourless, colourless, monatomic gases with very low chemical reactivity. The six naturally occurring noble gases are helium, neon, argon, krypton, xenon, and the radioactive radon,
So, we can say that all these elements are noble gases.
Therefore, option (B) is correct.

Note: The noble gases, in order of their density, are helium, neon, argon, krypton, xenon and radon. They are called noble gases because they are so majestic that, in general, they don't react with anything. For this reason, they are also known as inert gases.