Outer energy level is complete describes which property?

• A. Chemically stable
• B. Isotopes
• C. Chemical formula
• D. Periodic table

Answer: (A)

A full outer energy level means the valence shell is complete, giving the atom a very stable, low-energy configuration. When the outer shell is complete, there are no available spaces for bonding electrons, so the atom tends not to react—this is chemical stability. Elements with full valence shells (like the noble gases) are typically inert because they don’t need to gain, lose, or share electrons to become more stable.

Isotopes would involve different numbers of neutrons and mass, not a fuller outer shell. A chemical formula just shows which elements and how many atoms are present in a substance. The periodic table is a map of elements and their properties, not a description of a single property like stability.