Question

What is the atomic mass of an atom that has $6$ protons, $6$ neutrons and $6$ electrons?

Answer 1

Atomic mass of an element is the average weight of the atom of an element. Although the SI unit of mass is kilogram, atomic mass is measured in $atomic{\text{ }}mass{\text{ }}unit$ or $Dalton$, where $1$ Dalton is defined as $\dfrac{1}{2}$ of the mass of one carbon-$12$ atom. The protons and neutrons present in the nucleus account for nearly all of the total mass of the atom.

Complete answer:
We know the atomic mass of an atom is calculated by adding up the number of protons and neutrons present in the nucleus.
Given here, the number of protons is $6$ and the number of neutrons is also $6$.
$\therefore$ Atomic mass$=$number of protons $+$ number of neutrons$= 6 + 6 = 12$.
Therefore, the atomic mass of an atom that has $6$ protons, $6$ neutrons and $6$ electrons is $12$ $amu$.

Note:
While calculating the atomic mass of an atom, electrons are excluded because its weight is almost $1000$ times less than that of proton and neutron and is considered negligible. And another reason is to maintain stability while transferring any element from one orbital to another during the formation of compound electrons.