How can you tell if an element is a solid, liquid, gas or synthetic

It all depends on how high or low an objects melting point is. and solid, liquid, and gases are states of matter, you have to play with the temperatures of objects.

But most of the elements on the periodic table are solid at room temperature except gases hydrogen, nitrogen, oxygen, fluorine and chlorine, the “noble” gases helium, neon, argon, xenon, krypton and radon, and the liquids bromine and mercury. The only liquid elements at standard temperature and pressure are bromine (Br) and mercury (Hg). Although, elements cesium (Cs), rubidium (Rb), Francium (Fr) and Gallium (Ga) become liquid at or just above room temperature.

The mostly red pic are the solids, the pic with only two highlighted squared are liquids, the pic with the row of squares are the gases, and the last pic (with dark background) are the synthetic elements

Hope this helps.