| A | B |
|---|
| Sulphur dioxide | can be used as a preservative and to bleach wood pulp |
| Carbon monoxide | formed by the incomplete combustion of carbon-containing substances. |
| Oxygen | formed at the anode of the electrolysis of dilute sulphuric acid. |
| Hydrogen | has the atomic number of 1 |
| Ammonia | turns moist red litmus paper blue |
| Carbon dioxide | turns limewater chalky |
| Chlorine | greenish-yellow gas whose atom has 7 valence electrons. |
| Fluorine | in the same Group as chlorine but more reactive than chlorine. |
| Nitrogen | essential for plant growth |
| Argon | an inert gas |
