All solutions are mixtures, but not all mixtures are solutions.
Mixture is made up of two or more different kind of substances.
Mixtures may be homogenous or homogenous.
Solutions are considered as homogeneous mixtures.
For example, sand mixed with water makes heterogenous mixture but not a solution.
Sugar added to water makes the mixture which is homogenous and it is also a solution. Hence, not all the mixtures are solutions but all solutions are mixtures.