Q18 of 63 Page 113

An ion M2– contains 10 electrons and 10 neutrons. What are the atomic number and mass number of the element M? Name the element.

Number of electrons in M2- ion = 10

Number of neutrons = 10


Number of electrons in M atom = 10 – 20 = 8 electrons


Number of protons = atomic number = 8


Mass number of the element = 8 + 10 = 18u


The element is Oxygen and the ion is O2- oxide ion.


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