Question

In iron, the differentiating electron enters into the orbital of the penultimate shell.
A. True
B. False

Answer 1

Hint: To attempt this question, it is very important to note that electronic configuration of a particular atom, in this case it is Iron is filled according to a very specific set of rules which follows like, Aufbau’s principle, Pauli’s principle, Hund’s rule etc.

Complete step by step answer:
Iron has an atomic number of 26 which means if we try to put it or try to sort it out into different blocks or periods then, we will find that it belongs to the d-block of the periodic table which are also called as the transition elements with the electronic configuration of $(n-1){{d}^{1-10}}n{{s}^{1-2}}$. According to Aufbau's principle , the shells which have lowest energy will be filled first as compared to the higher energy ones. Therefore, the electronic configuration of Fe will look like this:
$Fe=\left[ Ar \right]3{{d}^{6}}4{{s}^{2}}$
If we see that last electron entered into the d-shell also known as the penultimate shell.

Therefore, this statement is true. Hence, the answer of this question is A. True.

Note: The outermost shell with electrons is called valence shell and similarly the shell which is inner to the valence shell is penultimate shell and the next inner shell to penultimate shell is anti-penultimate shell. Also, we have written the electronic configuration in the short form by comparing it to the Argon, if you don’t know about the electronic configuration till Argon whose atomic number is 18 then, it is suggested that you should go through its configuration once.