Saturated.
An unsaturated solution is a solution where more solute can still be added.
Number 4 is
-Oxidation occurs at the anode, while reduction occurs at the cathode. Recharging a battery involves the conversion of electrical energy to chemical energy. During recharging, there is movement of electrons from an external power source to the anode, and on the other side electrons are removed from the cathode.
Valence elections, electron affinity, electronegativity, atomic radius
The answer to your question would be D Volumetric Flask