Is skim milk a compound solution colloid element or alloy?

A colloid is a heterogeneous mixture in which the particles of one substance are dispersed throughout another substance in a more or less permanent suspension. The dispersed particles in a colloid are typically larger than those in a solution, but smaller than those in a suspension. Colloids can be classified according to the size of the dispersed particles.

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Skim milk is a colloid because it contains casein micelles, which are small particles of protein that are suspended in the milk. These particles are too small to be seen with the naked eye, but they are large enough to scatter light, which gives skim milk its characteristic appearance.