Atomic no. of calcium is 20. so its electronic configuration should be 2,8,10 as the M shell can accomodate 18 electrons.
Then why is it 2,8,8,2??
Calcium is just an example. I cant understand how Bohr's second rule can conflict with his 1st?
Kindly refer to the links given below:
https://www.meritnation.com/ask-answer/question/in-calcium-shell-m-has-only-8-electrons-while-a-max-of-18/structure-of-the-atom/3728137
https://www.meritnation.com/ask-answer/question/according-to-the-first-rule-of-bohr-and-bury-it-says-that/structure-of-the-atom/4065450
https://www.meritnation.com/ask-answer/question/in-calcium-shell-m-has-only-8-electrons-while-a-max-of-18/structure-of-the-atom/3728137
https://www.meritnation.com/ask-answer/question/according-to-the-first-rule-of-bohr-and-bury-it-says-that/structure-of-the-atom/4065450