Among the following, which is considered a state of matter?

• A. Solid
• B. Sublimation
• C. Viscosity
• D. Reactivity

Answer: (A)

A solid is indeed considered a state of matter. States of matter are distinct forms in which matter can exist, primarily classified as solid, liquid, gas, and plasma. Solids have a fixed shape and volume due to the closely packed arrangement of their molecules, which vibrate in place but do not move freely. This structural integrity allows solids to maintain their shape, making them easily recognizable as one of the fundamental states of matter.

On the other hand, sublimation refers to a physical process where a substance transitions directly from a solid to a gas without passing through the liquid state, rather than being a state itself. Viscosity is a measure of a fluid's resistance to flow, a property rather than a state of matter. Reactivity describes how likely a substance is to undergo a chemical reaction, which is also not a state of matter but rather a characteristic of substances when they interact with each other.