Question

Colour is imparted to glass by mixing:

• A. synthetic gas
• B. metal oxide
• C. oxide of non-metal
• D. coloured salts

Answer 1

The correct option is B metal oxide

Colour is imparted to glass by adding metal oxide like iron oxide in both oxidation states that is +2 and +3. Iron oxide ($FeO$) in the form of ferrous iron will give a bluish-green tint to the glass, whereas in its higher state of oxidation as ferric iron, it gives a yellowish-green tint, which can be masked by the addition of complementary colours such as red and blue. To ensure that most of any iron impurity is in its ferric state, oxidising agents such as sodium nitrate ($NaN{O}_3$) are added to the batch in small amounts.
Hence option $B$ is correct.