Why soft drink is a mixture but water is a compound?

You pour a bit of cordial, a strongly flavoured sugar syrup, into a glass, and fill the glass with water. You could also fill the glass with sparkling water to make a fizzy drink. Of course, this is how all fizzy drinks are made.

The base solvent is water, whose formula you know. The solutes are sugar (usually a lot of sugar), and the flavourings are from oranges, lemons, caramel, and a whole lot of other stuff. In fizzy drinks one of the solutes is carbon dioxide, with which a fizzy drink is supersaturated (this is why the drink fizzes).

Soft drinks are considered mixtures because they consist of multiple substances that are physically combined but can be separated by physical means. On the other hand, water is a compound because it consists of two or more different elements chemically bonded together in fixed proportions.