Rain as water vapour:
The rain tells the poet that she cannot be touched because she rises in the form of water vapour. This is the correct answer as it accurately describes the nature of rain and how it cannot be physically touched.

Water as rain:
Although water is a component of rain, it is not the reason why rain cannot be touched. Rain, in its liquid form, falls from the sky and can be felt or touched by humans. Therefore, option 'A' is incorrect.

Clouds:
Clouds are formed by the condensation of water vapour in the atmosphere, but they are not rain itself. Rain falls from the clouds, and the water droplets that make up the rain can be touched. Therefore, option 'C' is incorrect.

Explanation:
Rain is formed when water vapour in the atmosphere condenses and falls back to the earth in the form of water droplets. It is a natural process that occurs due to the water cycle. When the sun heats the surface of the earth, water evaporates and rises into the atmosphere as water vapour. This water vapour then cools and condenses to form clouds. Eventually, the water droplets in the clouds become too heavy and fall to the ground as rain.

Rain, in its liquid form, is tangible and can be touched. However, the rain in the poem is personified as a feminine entity and speaks metaphorically. The rain tells the poet that she cannot be touched because she is not physically present in the form of water droplets. Instead, she exists in the form of water vapour, which is invisible and cannot be directly touched.

Water vapour is a gaseous state of water that is not visible to the naked eye. It is the invisible form of water that rises into the atmosphere. Therefore, the rain, personified as a feminine entity, tells the poet that she cannot be touched because she exists as water vapour. This implies that the rain is ethereal and intangible in its true nature.

In conclusion, the rain tells the poet that she cannot be touched because she rises in the form of water vapour. This personification emphasizes the ephemeral and intangible nature of rain, highlighting its beauty and mystique.