Therefore, the correct option is (C) Magnesium ribbon on burning in air produces: 'Magnesium oxide, heat and light'.

Mercury is the only metal that is liquid at normal temperatures.

Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. The freshly cut surface is a shiny, silver colour, but this tarnishes quickly to a dull grey as the metal reacts with oxygen and water in the air.