Which one of the following is not a colloid ?

Which one of the following is not a colloid ?

Milk
Mud
Butter
Boric acid
This question was previously asked in
UPSC CAPF – 2016
The correct answer is Boric acid.
– Colloids are heterogeneous mixtures where the solute particles are dispersed evenly throughout the solvent as particles that are intermediate in size between those in true solutions and those in suspensions. Colloidal particles typically have a size between 1 nanometer and 1 micrometer.
– True solutions have particle sizes less than 1 nm. Suspensions have particle sizes greater than 1 micrometer, and the particles tend to settle out over time.
– Milk is an emulsion, which is a type of colloid where liquid droplets are dispersed in another liquid.
– Butter is also an emulsion, a type of colloid.
– Mud is primarily a suspension, where solid particles (soil, clay, silt) are dispersed in water. While mud can contain some clay particles of colloidal size, it is generally classified as a suspension because the larger particles settle out.
– Boric acid (H₃BO₃) is a molecular substance that dissolves in water to form a true solution. The particles in a boric acid solution are hydrated boric acid molecules, which are of molecular size, much smaller than colloidal particles.
The Tyndall effect (scattering of light) is a characteristic property of colloids, but not of true solutions. Suspensions may also scatter light, but they are unstable and settle. Boric acid solution will not show the Tyndall effect, unlike milk or muddy water (though settling occurs in mud).