Firstly, thinking about a qualitative question, there are many things we could ask. For example
Which would analyze whether the student knows or not that the electric field flows out of positively charged particles.
Thinking about a quantitative question, this can be achieved by asking things such as
This would evaluate whether the student knows concepts such as the one of net charge. In this situation we would have the following arrange
Thus, the atom has -2 of net charge.