12.Which orbital is filled after 6 S? a 4d b 4f c 4s d 4p

## Step 1<br />The problem is about electron configuration in atomic orbitals. The electron configuration of an atom is the distribution of electrons in its atomic orbitals. <br /><br />## Step 2<br />The order of filling of the orbitals is determined by the Aufbau principle, which states that electrons fill the lowest energy orbitals first. <br /><br />## Step 3<br />In the given problem, we are asked which orbital is filled after the 6s orbital. According to the Aufbau principle, the next orbital to be filled after the 6s orbital is the 4f orbital.