Serial Dilution
Serial Dilution is a way to make a liquid weaker step by step, mixing a small part into fresh liquid each time.
Think of it this way
You start with a dark red drink in a glass. You pour a spoonful into a fresh glass of water, making it lighter pink. You take a spoonful from that glass into another fresh glass, making it even paler. Each new glass holds less color because less dye mixes into more clean water each time.
Explaining serial dilution by grade level
Think about mixing a drop of soap into a cup of water. Now take a spoon of that mix and stir it into a new cup of clean water. Each new cup has less soap in it. You keep going until the water looks clear.