In everyday physical and chemical processes, which of the following is an example of an endothermic process that absorbs heat from its surroundings?

Introduction / Context:
Thermochemistry classifies processes as exothermic or endothermic depending on whether they release heat to the surroundings or absorb heat from the surroundings. Recognising which everyday phenomena fall into which category helps link theory with real life experience. This question contrasts processes like respiration and combustion with sweating, asking which one is endothermic and takes in heat rather than releasing it.

Given Data / Assumptions:

• Respiration is the biochemical process by which organisms release energy from food.
• Combustion and burning of natural gas are examples of burning fuels in air.
• Sweating involves the evaporation of sweat (water with salts) from the skin.
• Endothermic processes absorb heat; exothermic processes release heat.

Concept / Approach:
Respiration, combustion, and burning of natural gas are all exothermic processes. They release energy in the form of heat (and sometimes light) when chemical bonds in fuel molecules are broken and products with lower energy are formed. Sweating, on the other hand, involves the evaporation of water from the skin. Evaporation is an endothermic phase change: liquid water absorbs heat from the body and surroundings to change into water vapour. This absorption of heat cools the skin, which is why sweating is an important biological temperature control mechanism.

Step-by-Step Solution:
Step 1: Classify respiration. Respiration releases energy stored in glucose; it is an exothermic biochemical process. Step 2: Classify combustion and burning of natural gas. Combustion of fuels like wood, coal, or natural gas releases heat and light, making them exothermic. Step 3: Examine sweating. Sweating leads to evaporation of water from the surface of the skin, a process that requires absorption of heat to overcome intermolecular forces. Step 4: Identify which process is endothermic. Evaporation (and therefore sweating) absorbs heat, so sweating is endothermic.

Verification / Alternative check:
Thermodynamics tells us that phase changes like melting and evaporation require energy input: heat is absorbed to break intermolecular forces. This is why evaporation of sweat cools the skin; the necessary heat is drawn from the body and surrounding air. In contrast, combustion of natural gas (primarily methane) is described by reactions such as CH4 + 2O2 → CO2 + 2H2O + energy, where energy appears on the product side, signifying heat release. Similarly, cellular respiration releases energy stored in food molecules. This clear distinction confirms that sweating is the only endothermic process among the options.

Why Other Options Are Wrong:
Option A (Respiration): It is an exothermic process that releases energy from nutrients, used by the body for various functions. Option B (Combustion): Combustion of fuels is a classic exothermic reaction, giving off heat and often light. Option D (Burning of natural gas): Burning methane or other components of natural gas releases substantial heat and is clearly exothermic.

Common Pitfalls:
Some learners mistakenly consider any process connected with the human body as endothermic because they think energy is always being used. In fact, respiration supplies energy and is exothermic at the chemical level. Another confusion is not linking sweating with evaporation and phase changes. To avoid this, remember that endothermic processes feel cold or cause cooling because they absorb heat, such as evaporation, melting of ice, and the dissolution of some salts in water. Sweating fits this pattern perfectly.

Final Answer:
Among the given options, the endothermic process is Sweating, because evaporation of sweat absorbs heat from the body and surroundings.