**Statement 1 is incorrect:** Sand mining in riverbeds does not directly affect the salinity levels in the river water. Salinity is primarily influenced by factors like the inflow of saline water from the sea or other sources, dissolution of salts from surrounding rocks and soil and anthropogenic activities like irrigation return flows and industrial discharge. **Statement 2 is correct:** Sand plays a crucial role in natural filtration, helping to remove impurities from water percolating through riverbeds. Excessive sand removal can disrupt this filtration process, allowing pollutants to seep into groundwater, increase turbidity, making water more susceptible to contamination, expose toxic substances previously trapped in sediments. It can: **Statement 3 also correct:** Excessive sand mining can significantly disrupt the hydrological balance of a river system.
- Reduce water-holding capacity of riverbeds, leading to lower groundwater recharge.
- Cause river incision, deepening the riverbed and lowering adjacent groundwater levels.
- Affect agriculture and drinking water sources, particularly in arid and semi-arid regions. Hence, the correct answer is option (b) 2 and 3 only.