Can someone help me? We literally started this unit yesterday and I got quarantined so I dont have a clue what im doing..

Explanation:

Take out your periodic table.

The choices that have one 1 member of the periodic table on it are elements.

He is the symbol for Helium

O2 oxygen

C3 but this is really odd. It is Carbon but Carbon usually does not  combine in 3s.

The rest are all compounds (they are made up of the elements on the periodic table). For example

H2SO4

is made up of 2 Hydrogens

1 sulfur

4 oxygens.

All the others do exactly the same thing.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

the answer would be a