Question

The last orbit of argon would have electrons
A) 6
B) 2
C) 18
D) 8

Answer 1

Hint: Argon belongs to the class of noble gas positioned in the periodic table's 18^th group. Its atomic number is 18. And here, we have to write argon's electronic configuration first and then find out the count of electrons at the outermost shell.

Complete Step by Step Solution:
Let's discuss the element argon in detail. As stated above, it is a noble gas. And it is the most abundant noble gas. It is 0.00015% of the crust. And we know, the electrons are inserted in shells considering their energy level. The shells comprising lower energy levels are to be filled first, and then, the higher energy shells are filled.

We know that argon's atomic number is 18. So, argon has the electronic configuration of 2,8,8.
So, we see that the last orbit comprises eight electrons.
Hence, option D is right.

Additional Information: The 18^th group elements such as argon, helium, neon, etc. are termed inert gases because of their non-reactive nature. They are non-reactive because of the completely filled outermost shell. Among these inert gases, only xenon forms a large number of compounds with oxygen and fluorine. This is because of the larger size of the xenon atom. And, due to the large size, there is a weak attraction of the electrons to the nucleus which helps in compound formation.

Note: Aufbau principle helps to fill the electrons in an atom's different orbital. This rule states that the orbital comprising lower energy is to be filled first and then the orbital possessing higher energy is to be filled.