The maximum number of electrons in a d-orbital is 10
If you see a question that asks you the maximum number of electrons say in a d-orbital, would you say 10?
While answering this, you need to remember that a d-subshell has 5 orbitals and each orbital can hold a maximum of 2 electrons. So, one orbital will always hold a maximum of 2 electrons. But the d-subshell as a whole will hold a maximum of 10 electrons.
Similarly, each orbital in s and p will hold a maximum of 2 electrons only. But the total number of electrons in the s and p subshells will be 2 and 6 respectively.