Commonly used flux for brazing is

ANS:B - borax

Borax, also known as sodium borate, is a naturally occurring mineral compound that is commonly used for various industrial and household applications. It is composed of sodium, boron, oxygen, and water molecules. Borax has several properties that make it useful in different contexts:

1. Flux: In metalworking processes such as soldering and brazing, borax is used as a flux. Fluxes are materials that facilitate the flow of molten solder or brazing filler metal by removing oxides from the surfaces of the metals being joined. Borax dissolves metal oxides, promoting better wetting and adhesion between the metals and the solder or brazing material.
2. Cleaning Agent: Borax is an effective cleaner and degreaser. It is often used in household cleaning products, laundry detergents, and multipurpose cleaners due to its ability to dissolve dirt, grease, and stains. Borax can be used to clean various surfaces, including floors, countertops, and bathroom fixtures.
3. Fire Retardant: Borax has fire-retardant properties, making it useful in fireproofing materials such as wood treatments and textiles. When exposed to heat, borax releases water molecules, which help to extinguish flames and inhibit the spread of fire.
4. Insecticide: Borax is also used as an insecticide to control pests such as ants, cockroaches, and fleas. When ingested by insects, borax disrupts their digestive system and leads to dehydration, ultimately causing their death. Borax can be mixed with sugar or other bait to attract insects.

Overall, borax is a versatile compound with diverse applications in metallurgy, cleaning, fire safety, and pest control. However, it should be handled with care and used according to safety guidelines, as excessive exposure to borax dust or solutions can be harmful to health.