How is the atomic mass of an element calculated?

by taking the weighted averages of naturally occurring isotopes of that element

by determining the number of electrons in the outer orbital

by dividing its mass by that of the carbon-12 atom

by determining the number of protons in the nucleus

By taking the weighted averages of naturally occurring isotopes of that element.

Explanation:

We have to tell that how is the  calculate atomic mass of an element

In option A by taking the weighted averages of naturally occurring isotopes of that element.

It is true , we can calculate atomic mass of an element by taking weighted averages of naturally occurring isotopes , because average weight of an element is the mass which is calculated by summing the masses of an element's isotopes, each multiplied by its natural abundance on earth.

In option B

By determining the number of electrons in the outer orbital.

It is false because by calculating number of electrons in outer orbital we can calculate atomic number not atomic mass of an element.

In option C

By dividing its mass by that of the carbon 12 atom

It is false because we can not calculate and atomic mass of an element atomic mass is equal to mass .

In option D by determining the number of protons in the nucleus .

It is false because by determining proton we can calculate atomic number not atomic mass

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8