Are electrons located in the nucleus of an atom???

No, electrons are located outside the nucleus.

Explanation: An atom is made up of three particles: electrons, protons and neutrons. Electrons have negative charges, protons have positive charges while neutrons are uncharged, i.e., neutrons are neutral. Protons and neutrons are found in the nucleus of an atom and the sum of the number of protons and neutrons is known as the atomic mass of an element. Electrons are located outside the nucleus of an atom where they revolve round the nucleus in the electron orbits. The number of protons and electrons in a an atom is always equal, thus balancing the number of negative charges with the number of positive charges in an atom thereby making an atom electrically neutral.

layer 3 is younger than layer 6.