Among the major classes of biological molecules, which can be directly used as lamp oil or fuel because they are energy rich oils and fats?

Introduction / Context:
Biological molecules such as carbohydrates, lipids, proteins and nucleic acids have different structures and functions in living organisms. Some of them can also be used as fuels outside the body. Traditional lamps in many cultures have used plant oils or animal fats as lamp oil because these substances burn readily and release energy. This question asks you to identify which major class of biomolecules fits this description.

Given Data / Assumptions:

• The major classes listed include lipids, carbohydrates, proteins and nucleic acids.
• The focus is on use as lamp oil or fuel that can burn in air.
• Plant oils and animal fats are common examples of lamp oils.
• We assume ordinary combustion conditions.

Concept / Approach:
Lipids include fats and oils, which are largely composed of long hydrocarbon chains and ester linkages. These molecules are highly energy rich and hydrophobic. When burned in air, lipids react with oxygen to produce carbon dioxide, water and heat, making them effective fuels. Carbohydrates and proteins can also burn, but they are usually not used directly as lamp oils; carbohydrates are more commonly used as food energy, and proteins are crucial for structural and functional roles in organisms. Nucleic acids carry genetic information and are not used as fuels. The approach is to match the description of energy rich oils and fats to the correct biomolecule class.

Step-by-Step Solution:
Step 1: Recognise that traditional lamp oils include substances like vegetable oil, mustard oil and animal fat, all of which are lipids. Step 2: Understand that lipids store large amounts of chemical energy in their C–H and C–C bonds. Step 3: When lipids burn in air, they undergo combustion, releasing heat and light useful for lamps. Step 4: Carbohydrates like sugars and starches can also burn, but they are not typically used as lamp oils because they are often solid or water soluble, not oily fuels. Step 5: Proteins and nucleic acids are not standard fuels in lamps, and mineral ions cannot serve as combustible fuels in the same way. Step 6: Therefore, the class of biomolecules that can be directly used as lamp oil is lipids.

Verification / Alternative check:
Everyday examples support this conclusion. Cooking oils like sunflower oil and groundnut oil can be used in oil lamps. Ghee and tallow, which are animal fats, have also been used historically as lamp fuels. All of these are mixtures of triglycerides, which are typical lipids. Textbooks describe lipids as energy storage molecules that yield more energy per gram than carbohydrates when oxidised, explaining why they make efficient fuels. These observations confirm that lipids match the description in the question.

Why Other Options Are Wrong:
Option B, carbohydrates, includes sugars and starches that are usually solid or crystalline and not commonly used as lamp oil, although they can burn under certain conditions. Option C, proteins, are built from amino acids and are more valuable as structural and functional molecules than as fuels; they are not used as lamp oils. Option D, nucleic acids, are genetic material and are never used as ordinary fuels. Option E, mineral ions, are inorganic charged particles and do not burn as energy rich fuels. Only option A, lipids, consists of oils and fats that are suitable for use as lamp oil.

Common Pitfalls:
Some learners may think of carbohydrates first because they know carbohydrates are important energy sources in the diet. However, in the context of lamp oil, the key idea is hydrophobic, oily liquids that can burn steadily in a wick. Lipids fit this description, while carbohydrates are usually water soluble or solid. Remember that lipids are the main long term energy storage molecules and are well suited as fuels both inside organisms and in simple oil lamps.

Final Answer:
The class of biological molecules that can be used as lamp oil because they are energy rich oils and fats is Lipids.