My hen hatched 11 baby chick. 2 are white color 8 are brown and 1 is black color.
They are 2 weeks old. Since yesterday mama started rejecting her black one. She was attacking the baby chick like is her enemy.
I don’t know why suddenly she is acting crazy.
Tonight I separated the baby , any advise ?
I've never seen exactly that. I have had a couple of broody hens wean their chicks at 2-1/2 weeks old, but they weaned all of them, not just one or a few. I don't think that is it.
I once had a hen hatch a couple of red chicks. Two days later I gave her some red and black chicks freshly hatched. She accepted the red ones but rejected the black ones. I think that is because she had bonded with the first red chicks and those two black ones just looked different. That same hen had raised a mixed-color brood including red and black chicks earlier in the year, that's why I think bonding with the reds that hatch had something to do with it. She did not try to kill those black chicks, just drove them away.
I've never seen a hen reject a specific chick after she has cared for it for a couple of weeks. Are you sure the hen was the attacker? I once had a 2 week old chick kill a hatchmate and attack another while the hen watched. I've seen a broody hen peck a chick as discipline, such as telling it to get under her when she saw a possible threat. That requires some judgment on your part to tell the difference.
I've had hens raise as many as 18 chicks in warm weather. I don't know where you are in the world or what your weather is like but that should not have anything to do with it.
I don't know enough about your specific circumstances, your goals with chickens, how much room you have, or your set-up to give specific advice. If it were me I'd take another 2 or 3 chicks from that hen and try to raise them with the black one. Chickens are social animals and do much better if other chickens are around. You could take all eleven of them from her if you wish. I don't know why she rejected it but I'd give it a chance.
Good luck! This one is unusual in my experience.