Which of the following is chlorine isolated from by oxidation?

Brine

The correct answer is option 2. Brine .

Out of the listed options, chlorine is isolated from:

Brine (Sodium Chloride solution): This is the most common and commercially viable method for chlorine production. Electrolysis of brine (a solution of sodium chloride in water) separates chlorine gas (Cl₂) at the anode.

Chlorine is not typically isolated from:

The atmosphere: Chlorine is a very reactive element and doesn't exist freely in the atmosphere. It's mostly found combined with other elements like sodium (in NaCl) or potassium (in KCl).

Sylvite (Potassium Chloride): While KCl is a chlorine-containing compound, direct isolation of chlorine from it isn't a common practice. Brine, being more abundant and easier to process, is preferred.

Bischofite (Magnesium Chloride Hydroxide): Similar to Sylvite, Bischofite (MgCl₂•6H₂O) contains chlorine but isn't a primary source for chlorine isolation due to its lower abundance compared to brine.

Therefore, the correct answer is Brine.