Correct Option
The correct option is (b).
Explanation
The total volume of water on Earth remains constant. However, its availability and distribution vary spatially and temporally due to the hydrological cycle (water cycle), which involves the continuous movement of water through evaporation, precipitation, and runoff.
Statement-wise Analysis
- Statement (a) is Incorrect: The total volume of water on Earth is constant and does not change annually. It is a closed system where water changes state (liquid, solid, gas) but the aggregate quantity remains the same.
- Statement (b) is Correct: Water abundance appears to vary because it is in constant motion. It cycles through the oceans, the atmosphere, and the land. Consequently, the availability of water in a specific region fluctuates based on precipitation patterns and the movement of water within this cycle.
- Statement (c) is Incorrect: Fresh water accounts for only about 2.7% of the total water on Earth. The vast majority (approximately 97%) is saline water found in oceans and seas.
- Statement (d) is Incorrect: Only about 1% of freshwater is easily accessible and fit for human use (found in groundwater, rivers, and lakes). The remaining freshwater is locked in ice sheets and glaciers. Therefore, 70% of water is not fit for direct use.
Key Takeaway: While Earth's total water budget is fixed, local water availability fluctuates due to the dynamic nature of the hydrological cycle.