Answer
The positive and negative charge experience forces that differ both in magnitude as well as direction. Correct statement therefore is option (d)
Work Step by Step
Say the positive charge has magnitude $p$ and the negative charge has magnitude $n$. Given $p\ne n$
Force due to electric field $\vec{E}$ on charge $q$ is given by
$$\vec{F} = q\vec{E}$$
For the positive charge:
$$\vec{F_p} = p\vec{E}$$
For the negative charge:
$$\vec{F_n} = -n\vec{E}$$
Clearly $\vec{F_p}\ne\vec{F_n}$ both in magnitude as well as direction.