Which word describes something likely to change unpredictably?

The word "temperamental" accurately describes something that is likely to change unpredictably, often in reference to behavior, moods, or reactions that can vary widely without warning. When something is temperamental, it suggests an inherent volatility or capriciousness, making it difficult to anticipate how it will respond in different situations.

In contrast, "temperate" refers to a moderate climate or behavior, implying stability and consistency rather than unpredictability. "Truculent" describes someone who is aggressive or eager to fight, focusing on hostility rather than changeability. "Equanimous" denotes calmness and composure, especially in difficult situations, which is the opposite of being unpredictable. Hence, "temperamental" is the choice that aligns with the idea of variability and unpredictability.