Cell - Egg Cell
Tissue - Muscle tissue
Organ - Lung
Organ system - Respiratory system
Organism - Dog
Answer:
An atom is stable if the forces among the particles that makeup the nucleus are balanced. An atom is unstable (radioactive) if these forces are unbalanced; if the nucleus has an excess of internal energy. Instability of an atom's nucleus may result from an excess of either neutrons or protons.
Explanation: