Are rabbits solitary animals

No. Most rabbits are happier in a cage alone. In some cases a spayed/neutered rabbit will have no problem sharing a cage. However most rabbits are solitary.

A different answer (disagreement): Actually, rabbits are social animals.

In the wild they live in big groups (called "warrens" - this is also the name for the system of burrows and tunnels they live in).

Pet rabbits need a lot of companionship and socializing: if not from other rabbits, then from you (their owners). There are many benefits to keeping rabbits together, but they must be properly "bonded," which means they love each other and can be trusted not to fight. Rabbits need to be spayed/neutered before the bonding process starts. (Some people have successfully bonded two unspayed females raised from the same litter, but this isn't common.) When rabbits aren't spayed/neutered, they'll probably fight, or they'll breed. See the related question below for details and links about bonding.