1) The trails left by an electron as it moves around the nucleus
The electron model dictates that the electrons have no fixed position so it traces their path.
2) 8
Atomic number is equivalent to proton number
3) Its mass is lowered, but it is still the same element.
The element's identity is due to the number of protons; however, neutrons play a large role in an atom's mass. Thus, the mass will decrease but the element will be the same. Such variants are called isotopes.
Based upon Max Planck's theory of black-body radiation, Einstein theorized that the energy in each quantum of light was equal to the frequency multiplied by a constant, later called Planck's constant. A photon above a threshold frequency has the required energy to eject a single electron, creating the observed effect.