For a single atom with electrons in
all of these subshells, which of the following is the subshell occupied by the
lowest-energy electrons? Electrons-filled subshells in order
of increasing energy.
There are a number different rules
for which subshells are higher in energy than others, which are summarized using
this diagram. The question says that we have an
atom with electrons in all of the subshells given in this answer choices. So, let’s create an electron
configuration that would have all of these subshells, which we can do by following
the arrows in this diagram.
According to our diagram, the 1s
orbital comes first and two electrons can go in that subshell. The next is 2s, which can also have
two electrons. The next would be 2p, which can
have six electrons in that subshell in total, followed by 3s with our next two. 3p with the next six electrons,
followed by 4s, then the 3d subshell, which can accommodate 10 electrons, followed
by 4p and 5s. The 4d subshell would follow, then
5p, then 6s. And finally, our last answer choice
is 4f, which when full, accommodates a total of 14 electrons.
The question asked us which
subshells would be occupied by the lowest-energy electrons. And as we can see by filling our
orbitals in order of increasing energy, the lowest energy subshell that’s one of our
answer choices is 2s, which corresponds to answer choice (A).