The following question is from "The Official Guide to the HiSET Exam, Second Edition 2nd Edition", published by McGraw Hill, 2nd edition (March 25, 2016).2016 text, p. 75 (ISBN10: 1259640795).
Along with the question, students are given a periodic table (going up to element 109, Mt / meitnerium) that only contains element symbols (without atomic numbers or any other numbers).
Which group of elements has valence electrons in the same energy level?
A. B, Si, As, Te
B. Ga, As, Se, Kr
C. H, Li, Na, K
D. La, Pr, Os, Hg
The correct, given answer is B. I get this as all elements are on energy level 4.
But why is choice D not correct? To my understanding, all of these elements are on energy level 6 (and all seem to have valence electrons on 6th level).
Is the book incorrect or am I missing something?
I'm good with all the other chemistry questions and can explain them to the students. I'm stuck on this one and text fails to explain the answer. Again I think I understand why B works, but don't understand fully why D can't. Both answers feature elements each a part of the same respective horizontal row or energy level / period.