There are many colleges that accept 50% 12th marks. The minimum requirements of top colleges like Nit warangal and etc are 60% but there are alot of good colleges that accept 50% marks also. So no need to worry you can surely apply for MCA. This slab also vary for different quota in some colleges. So if you could provide me with more specific details like your deired college and Quota i can provide you with more accurate information.