Question

The electronic configuration of a transition element in +3 oxidation state is [Ar]3d7. Find out its atomic number.​

Answer 1

The atomic number of Ar is 18

3d7 means you have another 7 electrons.

+3 charge means a neutral atom of the material would have another 3 electrons.

Total = 28. What element has the atomic number 28.

Answer 2

Answer: Atomic number of transition element is 28.

Explanation:- A neutral element X with atomic number Z contains Z electrons and Z protons.

$X^{3+}$ is formed when 3 electrons are removed from the outermost shell. The given ion has configuration in terms of noble gas configuration is: Argon is the nearest noble gas which contains 18 electrons and thus

$X^{3+}:[Ar]3d^7$

Thus in order to get the neutral element we need to add three electrons and the configuration will be :

$X^{3+}:[Ar]3d^{10}$

thus the electrons are 28 and the atomic number is also 28.