Single Choice

The electrons configuration of a dispositive ion $$M^{2+}$$ is 2, 8, 14 and its mass number is 56. The number of neutrons present is :

A32
B42
C30
Correct Answer
D34

Solution

The electrons configuration of a dispositive ion $$M^{2+}$$ is 2, 8, 14.
Total number of electrons in the ion $$\displaystyle = 2+8+14=24$$.
The neutral atom loses 2 electrons to form dipositive ion.
Total number of electrons in the neutral atom $$\displaystyle = 24 + 2 = 26$$. The atomic number is equal to the number of electron in the neutral atom. It is 26.
Its mass number is 56. The number of neutrons present is equal to the difference in the mass number and the atomic number. It is $$\displaystyle 56-26=30$$.

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