Answer:
a. without completing 2p stuff...electrons cant go to 3s. the correct configuration is
1s2, 2s2, 2p6, 3s1
b. after 4s, 3d comes not 4d. the correct configuration is 1s2, 2s2, 2p6, 3s2, 4s2, 3d6
c. after 4s, it is 3d and then 4p the correct configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6.
Hope it helps you ｡◕‿◕｡
