In basic science, the gaseous form of water present in the air and produced during evaporation and boiling is called:

Introduction / Context:
This general science question tests your understanding of states of matter and the terminology used for water in different forms. Water is commonly observed as a liquid (in rivers, lakes, and taps) and as a solid (ice), but it also exists as a gas. Knowing the correct term for the gaseous form of water is important in topics like weather, climate, and the water cycle.

Given Data / Assumptions:

• The question focuses on the gaseous form of water, not the liquid or solid state.
• Options include water vapour, methane, humidity, and propane.
• Basic school level knowledge of the water cycle and gases in the atmosphere is assumed.

Concept / Approach:
Water can change from liquid to gas through processes like evaporation and boiling. When water molecules escape from the liquid and move freely in the air, water is said to be in the gaseous state. This gaseous form is called water vapour. It is usually invisible; what we see as clouds or steam are actually tiny droplets of liquid water suspended in air, not pure water vapour. Humidity is a measure of how much water vapour is present in the air, often expressed as relative humidity in percent. Methane and propane are completely different substances; they are hydrocarbon gases used as fuels and do not represent water in any form.

Step-by-Step Solution:

Verification / Alternative check:
Textbooks on weather and climate refer to water vapour as the gaseous phase of water and explain that it is a key greenhouse gas influencing the Earth energy balance. They describe humidity as the amount of water vapour present in the air, often measured with a hygrometer. Chemistry texts also discuss phase changes of water, noting that when liquid water boils at 100 degrees Celsius (at standard pressure), it turns into water vapour. Nowhere do they call methane or propane forms of water, confirming that water vapour is the only correct answer in this context.

Why Other Options Are Wrong:

Methane, a flammable hydrocarbon gas, is wrong because methane (CH4) is a separate compound used as a fuel and is not related to water changing state.

Humidity, a measure of how much water vapour air contains, is incorrect as a name for the gas itself; it describes a condition of air, not the gaseous form of water.

Propane, a fuel gas used in cylinders and burners, is wrong because propane (C3H8) is another hydrocarbon fuel, not water in gas form.

Common Pitfalls:
Students sometimes confuse the term humidity with the substance itself and may think humidity is a gas. Another pitfall is taking the visible “steam” above boiling water as water vapour, when it is actually condensed tiny droplets. To avoid these errors, remember that water vapour is the invisible gaseous form of water, humidity is a measure of how much of it is present, and gases like methane and propane are entirely different chemicals.