In the region where river joins the sea, salinity of water depends on

Options

A. Seasons
B. Altitude
C. Climate
D. Gravity

Answer

### Step-by-Step Solution:

1. **Understanding the Context**: The question asks about the factors affecting the salinity of water in estuaries, which are regions where rivers meet the sea.

2. **Identifying the Options**: The options provided are:
- A) Season
- B) Altitude
- C) Climate
- D) Gravity

3. **Analyzing Each Option**:
- **Option A: Season**: The salinity of estuarine water can vary significantly with the seasons due to changes in temperature, rainfall, and river flow. During hot weather, evaporation increases salinity, while during rainy seasons, freshwater influx can decrease salinity.
- **Option B: Altitude**: This refers to the height above sea level. While altitude can affect climate, it does not directly influence salinity in estuaries.
- **Option C: Climate**: Although climate affects the overall weather patterns and can indirectly influence salinity, it is not as immediate or variable as seasonal changes.
- **Option D: Gravity**: Gravity affects water flow but does not directly influence salinity levels in estuaries.

4. **Conclusion**: After analyzing the options, it is clear that the salinity of water in estuaries primarily depends on seasonal changes. Therefore, the correct answer is **A) Season**.