Which statement is correct about electron orbitals and energy levels? Which statement is correct about electron orbitals and energy levels?
A. Yttrium, $\ce{Y}$ ($Z = 39$) is the first element in the periodic table with an electron in a f sub-level.
B. The maximum number of electrons in one d orbital is 10.
C. The maximum number of electrons in the 4th main energy level is 18.
D. In a main energy level, the sub-level with the highest energy is labelled f.

I thought B and D are all possible solutions to this answer.
B--the maximum number of electrons in 1 d orbital is 10.
D--in main energy level, the sub-levels in order of increasing energy is s $&lt;$ p $&lt;$d $&lt;$f
So why is the answer only D?
Please advise and sorry in advance for the wrong tags or title name, as I am new to the group and am trying to improve on it.
Although @orthocresol got this first, and it should be credited to him, I'm posting it as an answer.

In option (B), the statement is incorrect as it refers to $d$ orbitals, which can (according to Pauli's Exclusion Principle) hold 2 electrons each, rather than the $d$ subshell, which can hold 10 electrons, as it has a total of 5 $d$ orbitals which can hold 2 electrons each, and $5*2=10$.

Thus, only option (D) is correct.