In basic thermochemistry, which of the following common processes are correctly classified as endothermic, meaning that they absorb heat energy from the surroundings?

Introduction / Context:
In thermochemistry, processes are called endothermic when they absorb heat from the surroundings. This absorption often causes a temperature decrease in the nearby environment unless heat is supplied from outside. Many everyday changes, including phase changes and biological processes, can be endothermic. This question asks you to recognise which listed processes are endothermic and to distinguish them from exothermic examples like combustion. Knowing these differences helps in understanding energy flow in physical changes, solution formation and life processes.

Given Data / Assumptions:

• Process A: Melting of ice at its melting point.
• Process B: Dissolving potassium chloride (KCl) in water.
• Process C: Photosynthesis in green plants using light energy.
• Process D: Combustion of methane gas in air.
• Endothermic means net absorption of heat energy by the system.

Concept / Approach:
The key concept is that endothermic processes have a positive enthalpy change, because energy must be supplied to break bonds or increase molecular separation. Melting requires energy to overcome forces in a solid lattice. Dissolving certain salts like KCl also requires more energy to pull ions apart than is released when ions interact with water molecules, so the solution cools. Photosynthesis is a strongly endothermic process that uses light energy to convert carbon dioxide and water into glucose and oxygen. Combustion, however, is a classic exothermic process that releases heat and light.

Step-by-Step Solution:
Step 1: For melting of ice, heat is absorbed from the environment to convert solid water into liquid water at the same temperature, so this is endothermic. Step 2: When potassium chloride dissolves in water, the solution typically becomes colder because the energy required to separate ions in the crystal is greater than the energy released during hydration, so this is also endothermic. Step 3: Photosynthesis in plants uses light energy to convert low energy molecules (CO2 and H2O) into higher energy glucose; this is clearly an energy absorbing, endothermic process. Step 4: Combustion of methane is known to release heat and light, so it is exothermic and not part of the endothermic group. Step 5: Therefore processes A, B and C are all endothermic, which matches option E that groups them together.

Verification / Alternative check:
You can verify the classification by thinking about observed temperature changes. Ice melts when heat is supplied, and if you hold ice in your hand it feels cold because it is taking heat from your skin. When solid KCl dissolves in water, the beaker feels cooler, indicating heat absorption. Photosynthesis obviously needs continual input of solar energy for the reaction to proceed. In contrast, a burning methane flame can be used to heat water because it releases heat. These observations reinforce the conclusion that the first three processes are endothermic.

Why Other Options Are Wrong:
Option A includes only one endothermic process and ignores the other two. Option B focuses on just one process and is incomplete. Option C mentions only photosynthesis, again missing the other endothermic examples. Option D confuses things by bringing in combustion, which is exothermic. Only option E clearly states that all of the processes in options A, B and C are endothermic, which matches the correct thermochemical classification.

Common Pitfalls:
Students sometimes think that only chemical reactions can be endothermic or exothermic and forget that phase changes like melting and boiling also involve heat flow. Another common error is to assume that all dissolving processes are exothermic because some salts warm the solution, but the direction of heat flow depends on the balance of lattice and hydration energies. In biological contexts, learners may overlook that building complex molecules like glucose from simple ones usually requires an input of energy. Always relate the concept back to whether the surroundings gain heat or lose heat overall.

Final Answer:
The correct choice is All of the processes in options A, B and C are endothermic, because melting of ice, dissolving potassium chloride and photosynthesis all absorb heat energy from their surroundings.