Which of the following reactions is endothermic, meaning the activation energy leads to a net absorption of heat from the surroundings?

• A. Neutralization of HCl and NaOH: HCl + NaOH ightarrow NaCl + H_2O
• B. Photosynthesis: 6CO_2 + 6H_2O ightarrow C_6H_{12}O_6 + 6O_2
• C. Rusting of iron: 4Fe + 3O_2 ightarrow 2Fe_2O_3
• D. Combustion of methane: CH_4 + 2O_2 ightarrow CO_2 + 2H_2O

Answer: (B)

Verified step by step guidance

1. Understand the difference between endothermic and exothermic reactions: Endothermic reactions absorb heat from the surroundings, while exothermic reactions release heat.
2. Analyze the given reactions based on their typical energy profiles and everyday knowledge: Neutralization of HCl and NaOH, rusting of iron, and combustion of methane are known to release heat, making them exothermic.
3. Recognize that photosynthesis requires energy input (usually from sunlight) to convert carbon dioxide and water into glucose and oxygen, indicating it absorbs energy and is therefore endothermic.
4. Recall that activation energy is the minimum energy needed to start a reaction, but the overall heat change (enthalpy change) determines if the reaction is endothermic or exothermic.
5. Conclude that among the options, photosynthesis is the reaction where the activation energy leads to a net absorption of heat, making it endothermic.