Have a look at Why do same/opposite electric charges repel/attract each other, respectively? for an explanation of the attraction between charges (I'm using the word charge in the general sense). It looks long and intimidating at first glance but persist because it isn't really.

For there to be a gravitational repulsion there would have to be negative mass e.g. some object with a mass of -1 kg. Note that this is not the same as antimatter - antimatter has a positive mass just like normal matter. We have never observed any matter with a negative mass, and as Chris notes in his answer negative mass would violate all sorts of conservation laws so it probably doesn't exist.

See Does matter with negative mass exist? for a discussion of negative mass, or this search for more on the subject.

Have a look at Why do same/opposite electric charges repel/attract each other, respectively? for an explanation of the attraction between charges (I'm using the word charge in the general sense). It looks long and intimidating at first glance but persist because it isn't really.

For there to be a gravitational repulsion there would have to be negative mass e.g. some object with a mass of -1 kg. Note that this is not the same as antimatter - antimatter has a positive mass just like normal matter. We have never observed any matter with a negative mass, and as Chris notes in his answer negative mass would violate all sorts of conservation laws so it probably doesn't exist.

See Does matter with negative mass exist? for a discussion of negative mass, or this search for more on the subject.