How does sprinking of salt help in clearing the snow covered roads in hilly areas? Explain the phenomenon involved in the process.

Options

A. lowering in vapour pressure of snow
B. depression in freezing point of snow
C. increase in freezing point of snow
D. melting of ice due to increase in temperature by putting salt

Explanation

To understand how sprinkling salt helps in clearing snow-covered roads in hilly areas, we need to explore the concept of freezing point depression. Here’s a step-by-step explanation:

### Step 1: Understanding Freezing Point
- **Freezing Point**: The temperature at which a liquid turns into a solid. For pure water, this is 0°C (32°F).

### Step 2: The Effect of Salt on Water
- When salt (sodium chloride, NaCl) is added to ice or snow, it dissolves into its constituent ions (Na⁺ and Cl⁻) in the water that is present in the snow.

### Step 3: Depression in Freezing Point
- **Freezing Point Depression**: The phenomenon where the addition of a solute (like salt) to a solvent (like water) lowers the freezing point of the solvent. This occurs because the presence of solute particles disrupts the formation of the solid structure of ice.

### Step 4: Decrease in Vapor Pressure
- When salt is added to the ice, it decreases the vapor pressure of the solution. This is due to the fact that the solute particles occupy space and reduce the number of water molecules that can escape into the vapor phase.

### Step 5: Melting of Ice
- As a result of the decrease in vapor pressure, the freezing point of the water (or ice) is lowered. Therefore, at temperatures that would normally keep water frozen (0°C), the ice will begin to melt into liquid water because the freezing point has been depressed.

### Step 6: Clearing the Roads
- The melted water helps to clear the snow-covered roads. As more salt is added, more ice melts, making it easier to remove the snow and ice from the roads.

### Conclusion
- Thus, sprinkling salt on snow-covered roads effectively lowers the freezing point of water, causing the ice to melt and helping in the clearing of roads in hilly areas.