Question

10 g of KCl dissolved in 100 g of H2O. Which is the solute and which is the solvent? & how do I know?

Answer 1

the solvent is usually easy to tell because it's the substance that there is "more of".

a slightly more wordy explanation is that the resulting solution retains most of the properties of the solvent, not the solute. If you mix a solid salt with liquid water, you have a solution that "looks" mostly like water, then the solvent is water