2-7-1
<h3>Further explanation
</h3>
Electrons can move the shell up or down by releasing energy or absorbing energy
Excited electrons show higher electron transfer to the shell by absorbing energy
So it can be concluded that there are 2 conditions:
Ground state is the state of electrons filling shell with the lowest energy levels.
Excited state is the state of electrons which occupies a higher energy level
The state of excited electrons can be seen from the presence of electrons which do not fill the skin completely but fill the skin afterward
2-7-1
From its 8 electron configuration, filling 3 shells, 2 electrons in the firs shell, 7 electrons in the second shell and 1 electron in the third shell
the electrons in the third shell should fill the electrons in the second shell first according to Aufbau rule (lower energy shells)

Answer:
Both roots are imaginary roots.
Explanation:
Consider these things:
If we try to solve x²+1 = 0, notice that we aren't able to solve the equation in Real Number system because there are no negative outputs for quadratic function.
Remember that quadratic function has range greater or equal to the max-min value.
x-axis plane represents the solutions of that equation. If a graph intersects x-axis plane then it has a solution.
While a graph that doesn't have any intersects on x-plane, it means that the equation for that graph doesn't have real solutions but imaginary solutions.
As you may notice some of parabola graph has one intersect, two intersects or none. One intersect is one solution to the equation — Two intersects are two solutions of the equation and lastly, no intersects mean that no real solutions and remain only imaginary solution.
<span>ability to dissolve ionic substances is the answer</span>
The reaction will be: FeBr2 + K --> KBr + Fe
Balancing gives: FeBr2 + 2K --> 2KBr + Fe
The molar mass of FeBr2 is 55.85 + 2*79.9 = 215.65 g/mol.
We divide 40 g / 215.65 g/mol = 0.185 mol FeBr2
Based on stoichiometry:
(0.185 mol FeBr2)(2 mol KBr/1 mol FeBr2) = 0.370 mol KBr