Question 4 unsaved when writing electron configuration the 3d block comes after the 4s block. question 4 options: true false

True

Explanation:

According to Aufbau's principle "sublevels with lower energies are filled up before those with higher energies".

Sublevels do not fill up in numerical order but there is a certain manner in which they are filled. The pattern is shown below:

  1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p e.t.c

 We see that the 4s gets filled before the 3d sublevel.

the answer is c.the valence of the atoms combine .