What are three signs that a chemical change has occurred?

Which type of orbits are found in the principal energy level n = 2 a - s b - s, f c - s, d d - s, p e - s, p, d

Which process transfers heat from inside earth to its surface? convection currents in mantle pulling away of tectonic plates drawing in of tectonic plates convection currents in crust

Describe at least two advantages and two disadvantages of using hydropower as a source of energy.