Question

An iron M2+ contains 10 electrons and 12 neutrons. What is atomic number and mass no of elemeny M

Answer 1

It has 12 atomic number

Answer 2

 The element M²⁺ after losing 2 electrons has 10 electrons.

here 2 + means two electrons are lost.

So the element M had 12 electrons originally.
Even if the electrons are lost , the protons are the same.

no: of protons = no: of electrons(before losing electrons)
therefore ,
no: of protons will be 12

The atomic number(Z) of an element is the same as the no: of protons.

Atomic no: =  12

Mass number = sum of protons + sum of neutron
                       = 12 + 12
                       = 24

The element with atomic no: 12 is Magnesium