Electrons carry negative charge while protons carry positive charge. Two electrons ($e_1$ and $e_2$) and one proton (p) lie on a straight line, as shown. The directions of the electrostatic force due to $e_2$ on $e_1$, the electrostatic force due to p on $e_1$, and the total electrostatic force on $e_1$, respectively, are:
$e_1$ $e_2$ p
? -->, <-- , and <---
? <--, -->, and <---
? <--, -->, and -->
? -->, <--, and -->
? <--, <--, and <---