What is meant by the ground state of an atom? What is meant by the ground state of an atom? All of the quantum numbers have their lowest values (n = 1,ℓ = mℓ = 0). The electrons are in the lowest state allowed by the uncertainty principle. All of the electrons are in the lowest energy state, consistent with the exclusion principle. The principal quantum number of the electrons in the outer shell is 1.

Option (a) is the correct answer.

Explanation:

We know that ground state means in total electrons acquired by the element are present in their lowest energy level.

We calculate the azimutal numbers as follows.

                      n = l + 1

where,     n = principle quantum number  

                l = azimuthal quantum number

Values of n can be 1, 2, 3, 4 and so on. Whereas the values of l can be 0, 1, 2, 3, and so on.

Also, "m" is known as magnetic quantum number whose values can be equal to -l and +l.  

So, when n = 1 then l = 0 and m = 0.

When n = 2 then l = 1 and values of m will be equal to -1, 0, +1. As it is given that the magnetic quantum number ml = -1. Hence, it is only possible when n = 2.

And, n = 1 is the lowest energy level. Therefore, we can conclude that the ground state of an atom means all of the quantum numbers have their lowest values (n = 1,ℓ = mℓ = 0).