Note the following:
1. A substance solidifies (becomes solid) when its temperature falls below the melting point.
2. A substance becomes liquid when its temperature is higher than the melting point but is lower than the boiling point.
3. A substance becomes gas when its temperature is higher than the boiling point.
Given:
The room temperature is 20°C. This is the temperature of the substance.
Let us identify substances A, B, and C.
Substance A is a solid.
For iodine, 20°C < 110°C (its melting point), iodine is substance A.
Therefore iodine is a solid.
Substance B is a liquid.
For bromine, 20°C > -7.2°C (its melting point), and also 20°C < 59°C (its boiling point).
Therefore bromine is a liquid.
Substance C is a gas.
For chlorine, 20°C > -35°C (its boiling point), therefore chlorine is a gas.
Answer:
Substance A is iodine.
Substance B is bromine.
Substance C is chlorine.
