Question

Name two gases which combine to form a liquid.

Answer 1

The gases change to liquid through the process of condensation. Condensation is a process in which the two or more molecules get combined to form a large molecule. Condensation is also the process in which the gaseous state of the substance changes to the liquid state. In this process the physical state of substance gets changed.

Complete answer:
When hydrogen gas and oxygen gas get combined together water, the liquid is formed. The water is formed by the process of condensation. In this process the gas loses its energy as its force of attraction between the molecules is weak thus changing into the liquid state.
Water can be present in liquid state, solid state and gaseous state. In solid state it is ice, in liquid state it is water and in gaseous state it is water vapor. When the liquid state of water is changed to solid then it undergoes the process of freezing. In this process the liquid state of the substance cools below the freezing point and loses the energy. When the solid state of water is changed to a gaseous state then it undergoes the process of sublimation. When the liquid state of water is changed to a gaseous state then it undergoes evaporation. In this process the liquid state of the substance gains the energy to overcome all the attracting force thus changing to a gaseous state. When the solid state of water is changed to liquid state then it undergoes melting. In this process the solid gains the energy to overcome the strong bonds and changes the bond into weak bonds thus changing the state of substance to liquid.

Note: The gaseous state of the substance can be changed into solid state by the process called frost formation. In this process the surface temperature of the material is lower than dew point, and heat transfer will make the water vapor in a humid environment thereby condensing them on exposed surfaces forming a frost.