You want to decorate the bottom of an aquarium with brightly colored rocks of different shapes and sizes. this describes a

Thank you for posting your question here at . I hope the answer will help you. Feel free to ask more questions.
Below are the choices:

homogenous mixture 
heterogeneous mixture 
semi mixture

You want to decorate the bottom of an aquarium with brightly colored rocks of different shapes and sizes. this describes a homogenous mixture 

The word hetero means different. Since the rocks are varied i assume it would be a heterogeneous mixture.