Question

what are the four properties that can be used to classify elements?

Answer 1

I get perturbed that someone has told you that there are four properties that can be used to classify elements. Total nonsense. Classifying elements is arbritrary.

Common ways include
By families, which have similar chemical and physical properties.
By metal or non metal character.
By atomic number
By atomic mass(this was the original way Mendelevv classified them).
By physical state at room temperature (solid, liquid, gas)
By nuclear stability

Answer 2

There are actually quite a few that can be used to classify elements:
- name
- atomic weight
- atomic mass
- chemical symbol (eg. Magnesium is Mg)
- metal or non-metal
- physical state (solid, liquid or gas)

Hope this helps! If your keen to have only 4
i would say the first 4 i have listed are the most important.