Solution:
The mass number of an element, denoted as A , is given by the sum of the number of protons (atomic number Z ) and the number of neutrons (symbolized as N ). The relationship can be expressed as:
A=Z+N
In this case, the mass number A is 175 and the number of neutrons N is 104. To find the atomic number (Z), we can rearrange the equation as:
Z=A−N
Substituting the given values:
Z=175−104=71
So, the atomic number Z of the element is 71 , which corresponds to the element Lutetium ( Lu ) in the periodic table. Lutetium has an atomic number of 71 , meaning it has 71 protons and, in a neutral atom, 71 electrons.
The arrangement of electrons in the orbitals follows the Aufbau principle, which states that electrons occupy the lowest energy orbitals available. The order of filling the orbitals is generally given by the sequence dictated by the increasing energy levels:
1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p,7s,5f,6d,7p
For elements with an atomic number of 71 , the electron configuration is:
[Xe]4f145d16s2
Here, [Xe] represents the noble gas core for Xenon (atomic number 54 ). Beyond this core, the electrons fill the 4f,5d, and 6 s orbitals.
From the given electron configuration, the last electron enters the 5d orbital.
Therefore, the correct answer is:
Option C
5d
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