Explanation:
Molecules of compounds are are compounds composed two or more than two different elements.
Molecules of an elements are made up two or more than two numbers of same type of atoms
(a) 
It is compound composed of sulfur and oxygen element.
(b) 
It is a molecules of a single element made up of 8 sulfur atoms.
(c) Cs
It is a symbol of an element named cesium.
(d) 
It is compound composed of nitrogen and oxygen element.
(e) O
It is a symbol of an element named oxygen.
(f)
It is a molecule of a single element made up of 2 oxygen atoms.
(g) 
It is a molecule of a single element made up of 3 oxygen atoms.
(h)
It is compound composed of carbon and hydrogen element.
(i) KBr
It is compound composed of potassium and bromine element.
(j) S
It is a symbol of an element named sulfur.
(k) 
It is a molecule of a single element made up of 4 phosphorus atoms.
(l) LiF
It is compound composed of lithium and fluorine element.