Question

Copper configuration 4s13d9 becomes 4s13d10 give reason

Answer 1

as the second is more stable configuration

so cu will try to attain that

Answer 2

Bec. The atom becomes in a more stable state when its energy sublevels are completely filled or half filled with electrons where its electronic configuration is 4s1,3d10 instead of 4s2,3d9. so that, the 4s sublevel is half filled with electrons and th 3d sublevel is completely filled with electrons