Electric force on negative charge opposes field direction

Steps:

• Recall force formula: $\vec{F} = q\vec{E}$.
• For negative $q$, $\vec{F}$ direction is opposite to $\vec{E}$.
• Given $\vec{F}$ points right on negative charge.
• Thus, $\vec{E}$ points left.

Why A is correct:

• By $\vec{F} = q\vec{E}$, negative reverses direction, so rightward force means leftward field.

Why the others are wrong:

• B: Rightward field would produce leftward force on negative charge.
• C: Downward field unrelated to horizontal force.
• D: Upward field unrelated to horizontal force.

Final answer: A