Which statement correctly describes an endothermic reaction?

• A. It releases energy as heat and becomes self-sustaining.
• B. It absorbs energy in the form of heat and requires additional heat input to continue.
• C. It neither absorbs nor releases heat.
• D. It only occurs in gaseous systems.

Answer: (B)

Endothermic reactions absorb energy from their surroundings, typically in the form of heat. Because energy is entering the system, the surroundings often feel cooler, and the reaction can continue only if heat is supplied. The statement that describes this exactly says energy is absorbed as heat and additional heat input is needed to keep the reaction going. The other ideas don’t fit: releasing heat describes an exothermic process, not endothermic; a process with no heat exchange isn’t endothermic; and endothermic reactions aren’t limited to any one phase of matter—they can occur in solids, liquids, or gases.