If a negatively charged particle is placed inside a uniform electric field the electric force that will act on that particle points in what direction in reference to the electric field lines?

opposite direction

Explanation:

An electric field is defined as a physical field which surrounds the electrically charged particles that exerts force on the other particles on the field.

Now when an electron or a negatively charged particle enters a uniform electric field, the electric forces acts on the negatively charged particles and it forces the particle to move in the direction which is opposite to the direction of the field. In an uniform electric field, the field lines are parallel.

Explanation:

negatively charged particle is placed inside uniform electric field

The force on the charge due to the electric field is

F = q E

when the charge is negative so the force on the charge is opposite to the direction of electric field.

The electric field is opposite to the force.