What os the term for the smallest bit into which chemical substance can be divided and still have the properties of that substance a : eletron b: molecule c: atom d: ion

That's a molecule of the substance.  You can break the molecule down further, into the atoms that make it up, but those don't have the properties of the original  'compound'.

Here's an example:

-- Sodium is a soft, slippery metal, that explodes when water touches it.

-- Chlorine is a poisonous green gas.

When an atom of Sodium and an atom of Chlorine combine, they make one molecule of a substance called "Sodium Chloride".  That's SALT !  It isn't green, it isn't a gas, it isn't poisonous, it isn't soft and slippery, and it doesn't explode when water touches it.

a 2,000 calorie based diet.