A
B
C
D
1

K2S

potassium sulfide

1

HCl

hydrochloric acid

1

Mn

manganese

1

H2CO3

carbonic acid
2
F2

fluorine

2

CO

carbon monoxide

2

P4

phosphorus

2

SO2

sulfur dioxide

3

NH3

ammonia

3

NaOH

sodium hydroxide

3
BaSO4
barium sulfate
3

NH4Cl

ammonium chloride

4

SO3

sulfur trioxide

4

CaCO3

calcium carbonate

4

CuCl2

where Cu is a Cu2+ ion

copper (II) chloride

4

CH4

methane