Metastable describes which concept?

• A. A theoretical state that rarely occurs
• B. A state that is theoretically unstable but regarded as stable due to its longevity
• C. A highly radioactive phase
• D. A completely stable permanent form

Answer: (C)

Metastable describes a state that isn’t the lowest-energy arrangement, but lingers for a long time because there’s an energy barrier to reaching the true ground state. Because it persists far longer than typical unstable states, it can be treated as effectively stable over practical timescales. So, the best fit is the description of a state that is theoretically unstable yet appears stable due to its longevity. The other choices miss the essence: metastability isn’t about rarity, it isn’t simply a completely stable permanent form, and it isn’t defined by being highly radioactive.