Hot cocoa is a homogeneous mixture. Homogeneous mixtures have uniform composition and properties throughout and are known as solutions. For e.g, when sugar/salt is dissolved in water it forms a solution in which the sugar/salt and water are uniformly mixed (the sugar is dissolved uniformly in water). e.g.air Heterogenous mixtures are those which aren't uniform in composition and properties throughout e.g. granite which consists of quartz, feldspar and mica and you can identify each of the substances separately in the mixture.
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