In Bohr's atomic model, he proposed that the electrons are revolving around the nucleus in their respective orbitals. There are 5 kinds of orbitals: the s, p, d and f orbitals. They differ in their energy level, shape and number of subshells. Each subshell holds two oppositely spinning electrons. The s has 1 subshell, p has 3, d has 5 and f has 7. You arrange the orbitals into energy levels just like how you write them in an electronic configuration.
In the first energy level, you only have one 1s orbital. In the second energy level, you have one 2s and one 2p orbital, the 2p having more energy than 2s. The other levels are shown in the picture.
For q3 to be in equilibrium the total force acting on it has to be zero.
Let's say that total distance traveled by car is L (this is just for the convenience).
We can set up a system of equations to find an answer. Let's say that from q1 to q3 the distance is r_1 and from q3 to q2 the distance is r_2, we know that this distance has to be equal to:

The second equation is going to the total force acting on the charge q3:

k_c is the Coulomb's constant. Since left-hand side is zero we just divide whole equation with k_c to get rid of it:

Let's solve this for r_1^2:

Now we have a quadratic equation with following parameter:

We know that two solutions are:

We need a positive solution. When we plug in all the numbers we get:
B) Electrons have the least amount of mass
Answer: Use less water
only turn on lights when needed
electrical cars
less gas usage
Explanation: