Which of the following processes is classified as exothermic?

• A. Melting of ice (H_2O_{(s)} → H_2O_{(l)})
• B. Combustion of methane (CH_4 + 2 O_2 → CO_2 + 2 H_2O)
• C. Photosynthesis (6 CO_2 + 6 H_2O → C_6H_{12}O_6 + 6 O_2)
• D. Evaporation of water (H_2O_{(l)} → H_2O_{(g)})

Answer: (B)

Verified step by step guidance

1. Understand the definition of an exothermic process: it is a chemical or physical change that releases heat to the surroundings, meaning the system loses energy.
2. Analyze the melting of ice (H_2O_{(s)} → H_2O_{(l)}): this is a phase change from solid to liquid, which requires energy input to break hydrogen bonds, so it is endothermic, not exothermic.
3. Consider the combustion of methane (CH_4 + 2 O_2 → CO_2 + 2 H_2O): combustion reactions release energy in the form of heat and light, indicating this process is exothermic.
4. Examine photosynthesis (6 CO_2 + 6 H_2O → C_6H_{12}O_6 + 6 O_2): this process requires energy input from sunlight to form glucose, so it is endothermic.
5. Look at evaporation of water (H_2O_{(l)} → H_2O_{(g)}): this phase change requires energy to overcome intermolecular forces, so it is endothermic.