Which of the following everyday materials is an example of a mixture rather than a pure substance?

Introduction / Context:
This question tests your understanding of the difference between pure substances and mixtures. Many everyday materials look uniform but are actually mixtures of several components. Recognising examples of mixtures helps you apply theoretical definitions of elements, compounds and mixtures to real world substances like milk, fuels and gases used in homes.

Given Data / Assumptions:

• Options: milk, gasoline, liquefied petroleum gas (LPG) and combinations of these.
• We must identify which of these are mixtures.
• Assume normal commercial forms of these materials, not chemically purified versions.

Concept / Approach:
A pure substance has a fixed composition and uniform properties throughout, and is either an element or a compound. A mixture is a physical combination of two or more substances in variable proportions. Milk is an emulsion of fats, proteins, lactose and minerals in water. Gasoline is a mixture of many different hydrocarbons. Liquefied petroleum gas is a mixture of propane, butane and sometimes other gases. Therefore, each of the listed substances is a mixture.

Step-by-Step Solution:
Step 1: Consider milk. Milk contains water, fats, proteins, lactose, minerals and vitamins. These components are not present in fixed chemical proportions and can be separated by physical methods such as centrifugation. Thus, milk is a mixture. Step 2: Consider gasoline. Gasoline is not a single compound but a carefully blended mixture of many hydrocarbons, including alkanes and aromatic compounds. The exact composition can vary between refineries and fuel grades, which is characteristic of a mixture. Step 3: Consider liquefied petroleum gas. LPG is typically a mixture of propane and butane, sometimes with small amounts of other gases. The proportions can vary depending on climate or supplier. This again is a mixture, not a single compound. Step 4: Since all three substances are mixtures, the correct answer is that all options are correct.

Verification / Alternative check:
Another way to test whether a material is a mixture is to ask if its composition can vary and whether it can be separated into components by physical methods. Different samples of milk from different animals or brands will have slightly different fat and protein contents. Gasoline composition is adjusted seasonally to improve engine performance. LPG composition varies between countries. These variations are typical of mixtures, whereas pure substances like distilled water always have the same composition H2O.

Why Other Options Are Wrong:
Choosing any one of milk, gasoline or LPG alone as the only mixture would ignore the fact that the others also meet the definition. The option None of these is incorrect because all three are well known mixtures. Therefore, the only fully correct statement among the options is that all options are correct.

Common Pitfalls:
Students may mistakenly think that because gasoline and LPG are sold under standard names they must be pure substances. In reality, fuels are carefully formulated mixtures tailored for specific performance requirements. Similarly, the uniform appearance of milk might suggest a pure substance, but it is actually a colloidal mixture. Always relate back to the definition of a pure substance and ask whether composition is fixed and unique or variable and separable.

Final Answer:
Milk, gasoline and liquefied petroleum gas are all mixtures, so the correct choice is all options are correct.