Assertion: Gravitational force is always attractive in nature, while electromagnetic force can be attractive or repulsive.
Reason : Electromagnetic force dominates terrestrial phenomena.

Mass comes in one variety, there is no negative mass, but charge comes in two varieties (positive and negative). That is why gravitational force is always attractive and electromagnetic force can be attractive or repulsive. Gravitational forces dominates terrestrial phenomena and electric force is largely zero because matter is mostly electrically neutral . i.e., net charge is zero.