Which statement is correct about electron orbitals and energy levels?


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


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