Question

A certain isotope x2+ contains 48 electrons and 75 neutrons. what is the mass number for this element?

Answer 1

The most important identity of an element is its atomic number or number of protons. Electrons and neutrons may vary, but protons stay constant. To start with, when an element is neutral, the number of protons and electrons are equal. When the isotope is a positive ion, that means that the element gives away 2 electrons. So, if the electrons is 48, then that means it was originally 48 - 2 = 46 electrons. From the periodic table, element 46 is Palladium (Pd).

Answer 2

Answer : The mass number for this element is 125.

Explanation :

Isotope : It is defined as the element that have the same number of protons but have the different number of neutrons of each of the atom.

Atomic number is defined as the number of protons or number of electrons.

Atomic number = number of protons = number of electrons

Mass number is defined as the sum of number of protons and number of neutrons.

Number of neutrons = Mass number - Number of protons

As we are given :

Number of electrons in $X^{2+}$ ion = 48

Number of neutrons in $X^{2+}$ ion = 75

So, number of protons in $X^{2+}$ ion = 48

For neutral atom, the number of electrons will be:

Number of electrons = Number of protons in $X^{2+}$ ion + Charge

Number of electrons = 48 + (+2) = 48 + 2 = 50

Now we have to determine the mass number for this element.

Number of neutrons = Mass number - Number of protons

Mass number = Number of neutrons + Number protons

Mass number = 75 + 50

Mass number = 125

Therefore, the mass number for this element is 125.