2 physical properties you can use to distinguish water from alcohol,gold from aluminum,helium gases from gases

Answer 1

There are a bunch of physical properties you can consider: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity, viscosity, attraction/repulsion to magnets, thermal conductivity, electral conductivity, etc. Physical properties are those that can be observed or measured without changing the chemical nature of matter.

Water vs Alcohol: Smell, melting point, boiling point.
Gold vs Aluminum: Density, melting point, color.
Helium gases vs Other gases: Density (He is very light), melting point (He has the lowest melting point of any element).

I wouldn't use flammability/combustion because it's more a chemical property (chemical transformation/reaction/change into another substance).

Answer 2

Alcohol is flammable, water freezes at 0C.
Gold is heavier than aluminum; gold is yellow aluminum is silver.
Helium is lighter than air; does not support combustion.