Question

The atomic number and atomic mass values of an element are 25 and 55. What is the number of electrons, protons and neutrons in its most stable ion?

• A. $25,25,30$
• B. $23,25,30$
• C. $22,25,30$
• D. $20,25,30$

Answer 1

The correct option is B $23,25,30$

Electronic configuration of an element having atomic number$=25$ is $\left[Ar\right]4s^{2}3d^5$. So the most stable oxidation state is $+2$ which results in the removal of two 4s electrons leaving an ion in which all five of $3d$ orbitals contain single electron. So the most stable ion contains $23$ electrons.

A number of protons are equal to its atomic number i.e., $25$.

Atomic mas = Number of protons + Number of neutrons

$55=25$ + Number of neutrons

Number of neutrons$=30$