ANS:B - Rain water

Rain water is generally considered the purest form of water among the options listed. Rain water is generally considered the purest form of water among the options listed for several reasons:

Natural Filtration Process:

1. Evaporation and Condensation:
   • Rainwater forms through the evaporation of water from oceans, rivers, and lakes, which leaves behind impurities. As it condenses in clouds, it can be relatively free of contaminants.

Low Contaminant Levels:

1. Minimal Minerals and Chemicals:
   • In its initial form, rainwater contains fewer dissolved minerals and chemicals compared to groundwater or surface water, making it more "pure."

Collection and Use:

1. Harvesting Practices:
   • When collected properly, rainwater can be used for various applications, including irrigation and even drinking, after appropriate filtration and treatment.

Comparison to Other Water Sources:

1. Underground Water:
   • Often contains minerals and contaminants from the surrounding soil and rock layers.
2. Well Water:
   • Similar to underground water, well water can have higher levels of dissolved solids and microorganisms, depending on the depth and location.
3. Lake Water:
   • Typically contains various organic materials, sediments, and pollutants, especially in populated areas, making it less pure than rainwater.

Summary:

Rainwater is considered the purest form of water because it undergoes natural filtration during the water cycle, resulting in lower levels of impurities compared to underground, well, and lake water. However, its purity can vary based on environmental conditions and air quality at the time of rainfall.