Final answer:
The electron configuration 1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^2 corresponds to 20 electrons. Quantum mechanics principles such as the Pauli exclusion principle and Hund's rule determine the filling of electron orbitals.
Step-by-step explanation:
The electron configuration of an atom describes the arrangement of electrons in its orbitals. The designated electron configuration refers to the number of electrons in each orbital. In this case, the electron configuration provided is 1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^2.
To determine the total number of electrons, we can add up the exponents of each orbital. The 1s orbital has 2 electrons, the 2s orbital has 2 electrons, the 2p orbital has 6 electrons (2 in each suborbital: px, py, pz), the 3s orbital has 2 electrons, and the 3p orbital has 6 electrons. Finally, the 4s orbital has 2 electrons. Adding these up, we get a total of 20 electrons.
These electron configurations and the filling of electron orbitals are determined by the principles of quantum mechanics. The Pauli exclusion principle states that no two electrons can have the same set of four quantum numbers. Hund's rule states that whenever possible, electrons retain unpaired spins in degenerate orbitals.