Question

Question #a14c2

Answer 1

`9 * a_0`

Explanation:

All you need to know in order to answer this question is that the radius of an orbit depends on the principal quantum number, `n`, that describes the energy level on which the electron is located.

If you take `a_0` to be the Bohr orbit, you can say that you have

`r_n = n^2 * a_0`

In your case, the third orbit is characterized by

`n = 3`

so you will have

`r_3 = 3^2 * a_0 = 9 * a_0`