What is a substance that cannot be separated into simpler substances by physical or mechanical methods such as filtering, boiling, or sifting?

Compounds are such substances that can't be separated by chemical means like potassium chloride, sodium chloride(common salt), potassium aluminium sulphate(alum).

what is the freakin anser

Why does a helium balloon float up?

Because it thought the sun was hot.

The substance you are referring to is called an "element." Elements are pure substances that cannot be broken down into simpler substances by physical or mechanical means.

To determine whether a substance is an element or not, you can consult the periodic table of elements. The periodic table contains a list of all known elements, each represented by a unique symbol. Elements are organized based on their atomic number (number of protons in the nucleus of an atom) and their chemical properties.

If a substance is listed on the periodic table as an element, it means it cannot be separated into simpler substances by physical or mechanical methods like filtering, boiling, or sifting.