An ionic bond results in an exchange or transfer of electrons between the 2 different types of atoms, most likely the metal atom and nonmetal one.
For example the compound NaF is held together by electrostatic forces of positive and negative charges due to the transfer of electrons from the sodium to fluoride atom.
Answer:
Water, fresher climate, not only scientific factors but also a psychological factor (nice beaches, palms, other wildlife, etc.)
Over time, as oxygen levels decrease, CO2 levels increase. Respiration is correct as it uses oxygen as a reactant and releases CO2 as a byproduct.