The state in which the particles of a substance are mixed with fluid but undissolved is called a suspension.

Here's why:

* Suspension: A suspension is a heterogeneous mixture where particles of a substance are dispersed throughout a fluid (like water or air) but do not dissolve. These particles are typically larger than those found in a solution and will settle out over time if left undisturbed.

* Examples: Sand in water, dust in the air, and milk are all examples of suspensions.

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