Is chocolate shake an element or a compound or a mixture?

It's an element. An element is a substance entirely consisting of one element on the Periodic Table like a gold ring or the oxygen in a oxygen tank. A compound is a substance that consists of chemicly bonded elements like water (H2O) or salt (NaCl). A Mixture is just a mix of various compounds and elements without a chemical bond. Examples of this are coins. Chocolate Shakes however are elements, and are number 55 on the periodic table with the symbol of Cs.

I hope this answered your question. =)