Which of the following statement is correct?

I. On combustion in excess of air, lithium forms mainly the oxide.

II. The alkali metal halides are all high melting, colourless crystalline liquids

Only I

The correct answer is option 3. Only I.

Here's a breakdown of why each statement is true or false:

I. On combustion in excess of air, lithium forms mainly the oxide.

This statement is true. When lithium burns in excess air, it primarily forms lithium oxide (Li₂O).

II. The alkali metal halides are all high melting, colorless crystalline liquids.

This statement is false. Alkali metal halides are generally high melting solids, not liquids. While they are typically colorless, some can show color depending on the specific element involved.

Therefore, only statement I is accurate.