A person mixes two liquids together as shown in the illustration below.

Substance X (mass 150g, clear) + Substance Y (mass 150g, clear)= clear yellow this is what it looks like in the cub )( also its solid and mass 300g
The person can conclude that there was a chemical change because

the mixture turned into a different color (clear yellow) compared to the original clear substances X and Y. This indicates a chemical reaction took place, resulting in new substances being formed. Additionally, the change in state from solid to liquid also suggests a chemical change occurred.