The neutral atoms have the same number of protons (positive charge) and electrons (negative charge). So in the periodic table the atomic number shows the number of protons and electrons.
Magnesium has an atomic number of 12, so it has 12 electrons. Electronic configuration shows the location of the electrons around the atom nucleus. To know its electronic configuration we will need to use the order of fill (the chart in the image), which indicates how the electrons are placed into the orbitals based on the order of their energy. The lowest energy orbitals (such as ) will be occupied first.
So according to this Magnesium electronic configuration will be as 2+2+6+2=12 electrons. The superscript of each orbital is the amount of electrons that occupied it.
Condensation releases energy when water vapor condenses to form water droplets. Evaporation absorbs energy whenever it changes from liquid to gas, the heat from the sun heats the water up and absorbs energy.