Which Of The Following Is Not Homogeneous Mixture

You're staring at a glass of iced tea. That said, the sugar dissolved minutes ago. The lemon slice floats near the top. Ice clinks against the side. It looks like one thing — a drink. But chemically? It's three different mixtures happening at once. And only one of them is truly homogeneous.

Most people learn the definitions in high school chemistry, then promptly forget them. But the difference shows up everywhere: in your morning coffee, the paint on your walls, the blood in your veins, the air you're breathing right now. Knowing how to spot a non-homogeneous mixture isn't just trivia. It changes how you cook, how you store food, how you read a lab report, and whether you trust that "well-mixed" bottle of salad dressing.

What Is a Homogeneous Mixture

A homogeneous mixture is uniform at the molecular level. Every sample you take — whether from the top, bottom, or middle — has the exact same composition and properties. You can't see the components. You can't filter them out. They don't settle over time.

The classic examples are solutions: salt dissolved in water, sugar in tea, carbon dioxide in soda (before you open it), brass (copper and zinc), sterling silver, the air in a room. In each case, the particles are individual molecules or ions, thoroughly intermingled. The mixture is a single phase.

But here's where it gets slippery. Some mixtures look* homogeneous to the naked eye but aren't. Practically speaking, milk. Mayonnaise. On the flip side, blood. Fog. Smoke. These are colloids — particles dispersed in a medium, but the particles are larger than molecules (1 nanometer to 1 micrometer). They scatter light (the Tyndall effect). They can be separated by centrifugation or ultrafiltration. They're technically heterogeneous, even if they pass the "looks uniform" test.

The Phase Rule

A true homogeneous mixture exists in one phase. Air is a gaseous solution. Solid, liquid, or gas — but only one. If you can see a boundary between phases — liquid-liquid, solid-liquid, gas-liquid — it's not homogeneous. Vodka is a liquid solution. Brass is a solid solution. That boundary means the composition changes across it.

What Is a Heterogeneous Mixture

Heterogeneous mixtures are non-uniform. You can see the different parts. They have distinct phases. The composition varies from spot to spot. Sand and water. Day to day, oil and vinegar. Granite. That said, trail mix. A bowl of cereal with milk. Worth adding: pizza. In real terms, concrete. Soil.

The components retain their individual properties. You can often separate them by physical means: filtration, decanting, magnetism, sieving, hand-picking. On the flip side, they separate. They settle. They're visibly "not one thing.

But the line blurs. On the flip side, a colloid sits in the middle. It looks* homogeneous. It acts* heterogeneous under the right test. That's why "which of the following is not a homogeneous mixture" is a favorite exam question — it catches the students who only memorized "uniform = homogeneous.

Why the Distinction Matters

In a kitchen, it determines whether your vinaigrette stays emulsified or breaks before it hits the salad. In pharmaceuticals, it decides whether a drug suspension needs shaking before every dose (heterogeneous) or delivers a consistent amount per mL (homogeneous). In environmental science, it tells you whether a pollutant is truly dissolved in groundwater or just suspended — which changes how it moves, how you sample it, and how you clean it up.

In materials science, homogeneous alloys like brass have predictable properties. Because of that, heterogeneous composites like concrete have strengths and weaknesses tied to their interfaces. In biology, blood is a heterogeneous mixture (cells in plasma) — and that heterogeneity is exactly why centrifugation works for diagnostics.

Get it wrong, and you might assume a mixture is stable when it's not. Or you might over-process something that was already uniform. Or you might filter a colloid thinking it's a solution, then wonder why your filter clogs instantly.

How to Tell Them Apart (Practical Tests)

You don't need a lab to run basic checks. Start with the simplest:

Visual inspection. Can you see distinct parts? Layers? Particles? Sediment? If yes → heterogeneous. But if no, don't stop here.

Light beam test (Tyndall effect). Shine a flashlight through the mixture in a dark room. A true solution (homogeneous) shows no visible beam. A colloid scatters the light — you see the path of the beam. A suspension (large-particle heterogeneous) may block it entirely or show heavy scattering.

Filtration. Pour through a coffee filter or lab filter paper. Solutions pass through completely. Colloids mostly pass through (though some may be retained by ultrafilters). Suspensions leave residue.

Centrifugation. Spin it. Solutions don't separate. Colloids may separate at high speeds (ultracentrifuge). Suspensions separate fast at low speeds.

Time. Let it sit. Solutions stay mixed indefinitely. Colloids can be stable for months or years (milk, ink, gelatin). Suspensions settle in minutes to hours.

Want to learn more? We recommend what is 75 as a fraction and ordeal in the abyss in the odyssey for further reading.

Magnification. Under a microscope (optical or electron), solutions show nothing but uniform medium. Colloids show dispersed particles. Heterogeneous mixtures show obvious distinct phases.

The Particle Size Scale

• Solutions (homogeneous): < 1 nm — individual molecules/ions
• Colloids (heterogeneous, but fine): 1 nm – 1 µm — nanoparticles, macromolecules
• Suspensions (heterogeneous, coarse): > 1 µm — visible particles, settle rapidly

This scale is why "looks uniform" fails as a definition. It passes the eye test. So it fails the Tyndall test. Milk is a colloid — fat globules and protein micelles in water. It fails the centrifugation test. It's not homogeneous.

Common Examples: Which One Is Not Homogeneous?

Let's run through a typical multiple-choice lineup. You've seen these before. The question: Which of the following is not a homogeneous mixture?

1. Salt water — homogeneous (solution)
2. Air — homogeneous (gaseous solution)
3. Brass — homogeneous (solid solution)
4. Milk — not homogeneous (colloid, emulsion of fat in water)
5. Vinegar — homogeneous (acetic acid solution in water)
6. Blood — not homogeneous (suspension of cells in plasma)
7. Sugar water — homogeneous (solution)
8. Smoke — not homogeneous (aerosol, solid particles in gas)
9. Fog — not homogeneous (aerosol, liquid droplets in gas)
10. Mayonnaise — not homogeneous (emulsion, colloid)
11. Granite — not homogeneous (heterogeneous solid mixture of minerals)
12. Gasoline — homogeneous (solution of hydrocarbons)
13. Soil — not homogeneous (heterogeneous solid mixture)
14. Stainless steel — homogeneous (

The boundary between a true solution and a colloid is not always obvious to the naked eye, yet the underlying particle dimensions dictate how the system behaves. When the dispersed entities are smaller than roughly one micrometre, they remain suspended indefinitely under ordinary conditions, giving the appearance of a single phase. Conversely, once the particles exceed that threshold, gravity begins to dominate and the mixture will separate unless continuously agitated.

In practice, many everyday substances occupy the middle ground. An aerosol such as fog or smoke consists of liquid droplets or solid particles that are finely dispersed in air; they scatter light strongly, so the beam of a flashlight becomes visible, yet they do not settle rapidly because Brownian motion counteracts gravity. A gel, by contrast, is a network of interconnected colloidal particles that traps the dispersion medium, producing a semi‑solid material that resists flow while still appearing uniform.

Understanding these distinctions has concrete implications. In the pharmaceutical industry, a drug formulated as a colloidal suspension must be shaken before use to re‑disperses the active particles, whereas a true solution can be poured directly. In food science, the stability of an emulsion like mayonnaise determines shelf life; breaking the emulsion results in a watery separation that signals a shift toward a coarser suspension. Environmental monitoring relies on the same principles: suspended sediments in rivers will settle in downstream calm zones, while dissolved nutrients remain uniformly distributed.

To recap, the key differentiators are particle size, stability, and the ability of the mixture to pass through filters or remain uniformly mixed over time. Solutions are molecular‑level dispersions that never separate, colloids are nanoscale assemblies that persist through Brownian motion, and suspensions are coarse dispersions that readily settle. Recognizing which category a mixture belongs to guides choices in processing, storage, and analytical techniques, ensuring that the appropriate method — whether filtration, centrifugation, or simple stirring — is employed.