Which of the following statements is true ?

The correct option is: All non-metals are non-ductile.

Let us analyze each of the given statements to understand why this is the true statement:

1. All metals are solids: This statement is incorrect because Mercury (Hg) is a metal that exists as a liquid at room temperature.

2. All metals are hard: This statement is incorrect because alkali metals like Sodium (Na) and Potassium (K) are very soft and can easily be cut with a knife.

3. All non-metals are gases: This statement is incorrect because non-metals exist in solid, liquid, and gaseous states. For example, Carbon and Iodine are solids, while Bromine is a liquid non-metal at room temperature.

4. All non-metals are non-ductile: Ductility is the property of a material to be drawn into thin wires. Non-metals are generally brittle in solid form and lack ductility. Therefore, all non-metals are non-ductile, making this statement true.