A student says: "A charge of 10 µC and a charge of 2 µC are 0.50 m apart…

Step 1. Is she right? No. By Newton's third law, the force on the small charge and the force on the large charge are equal in size and opposite in direction. In the formula $F = kq_1q_2/r^2$, the force depends on the product $q_1q_2$. It does not matter which charge we call big. The same force acts on both.

Step 2. Why does it feel unequal? The same force gives a bigger acceleration to the lighter body. That can make the small charge seem to do more of the moving, but the forces are equal.

Step 3. Double the distance. $r^2$ becomes $4$ times larger, so the force on each charge becomes a quarter.

Step 4. Double the $2\ \mu\text{C}$ charge. The product doubles, so the force on each charge doubles.