Which of the following method is used for the purification of water?

Reverse osmosis

The correct answer is option 2. Reverse osmosis.

Let us break down the process of reverse osmosis (RO) in detail and also clarify why the other options are not used for water purification.

Reverse Osmosis (RO) - Water Purification

Reverse osmosis is a process used for purifying water by removing contaminants, dissolved salts, and impurities. Here's how it works:

Osmosis is a natural process where water moves from an area of low solute concentration (e.g., fresh water) to an area of high solute concentration (e.g., salt water) through a semipermeable membrane.

In reverse osmosis, this process is reversed by applying pressure greater than the osmotic pressure to the side with higher solute concentration (e.g., salt water). Water molecules are forced through the semipermeable membrane, leaving behind the dissolved salts, chemicals, and other impurities.

The semipermeable membrane in the RO system has very tiny pores, allowing only water molecules to pass through while blocking larger molecules such as salts, minerals, and organic impurities.

Applications of Reverse Osmosis:

Desalination: Removing salt from seawater to make it drinkable.

Household water filters: Commonly used in home filtration systems for producing purified drinking water.

Industrial water treatment: Used to purify water for industries like pharmaceuticals and electronics manufacturing.

Key Benefits:

Effectively removes 99% of dissolved salts, bacteria, viruses, and impurities from water. Produces high-purity water suitable for drinking or specialized industrial uses.

Why the Other Options Are Not Used for Water Purification:

Ebullioscopic technique: This method is associated with boiling point elevation. It's used in chemistry to measure molecular weights based on how a solute raises the boiling point of a solvent. It has no direct application in water purification.

Osmosis: Osmosis is a passive process where water moves from a region of low solute concentration to high solute concentration through a semipermeable membrane. While osmosis naturally occurs in biological systems, it is not used for purifying water since it does not remove impurities—water moves toward the solute, not away from it.

Crystallization: Crystallization is used for purifying solid substances by converting them from a liquid solution into a pure crystalline form. It’s not suitable for purifying water, which is a liquid, because this method is primarily for separating out solids from liquids.

Summary:

Reverse osmosis is a powerful and effective method for purifying water by forcing it through a semipermeable membrane, leaving contaminants behind. This is why reverse osmosis is widely used in water treatment plants, home filtration systems, and desalination.

The other techniques mentioned (ebullioscopic technique, osmosis, and crystallization) are not suitable for water purification.