What defines the classification of a substance as a base?

A substance is classified as a base primarily due to its properties, one of which is its ability to have a slippery feel and its tendency to react with acids. Bases are characterized by having a pH value above 7, which contributes to their slippery texture, often felt when common bases like soap or baking soda are handled. This tactile property arises because bases can interact with fatty acids in our skin, producing this slippery sensation.

Moreover, bases can neutralize acids in a chemical reaction, producing water and salts. Their reactivity with acids is a defining characteristic of bases, as it demonstrates their fundamental role in acid-base chemistry. This behavior not only helps in identifying bases but also highlights their functional importance in various chemical processes, including those that occur in biological systems.

The other choices do not accurately define a base: a pH value below 7 characterizes an acid, being non-reactive does not describe any specific class of substances and being solid at room temperature is not a requirement for all bases, as many bases can exist in liquid or gaseous forms.