When you have two unlike charges in a line – where is the electric field the greatest? Is there ever a point where the field will be zero?

-Electric field will be the greatest at the point where it is closest to it's charges.

- No, there cannot be a point where the field will be zero

Explanation:

Usually, in field lines and vectors, the principle is that: Where the field lines are in a close manner together, the field will be strongest. However, where the field lines are in a manner far apart, the field will be the weakest.

Applying that to our question now it means that the electric field will be the greatest at the point where it is closest to it's charges.

In unlike charges, there can never be a field of zero in between the 2 opposite charges because the field vectors from both unlike charges will point towards the negative charge.