Careless mistakes are quite common among the JEE aspirants. The difference between the AIR-1 and AIR-10 is not the lack of knowledge, it's just the silly mistakes which could have been avoided.
This might happen due to focus on conceptual understanding. But through conscious efforts candidates can reduce these silly mistakes.
JEE aspirants must check out - How to Reduce Careless Mistakes in JEE Mains
Students need to pay attention on them and try to not to do these careless mistakes in the JEE Exam.