General Science - 2

Common salt (sodium chloride) is obtained from sea water by allowing the water to evaporate in large shallow pans, leaving the salt behind. Sublimation, crystallisation, and filtration are not the primary methods used for this large-scale extraction.

Water becomes hard as it flows over rocks because it dissolves minerals, specifically calcium and magnesium carbonates or sulfates. Calcium carbonate is the most common contributor to temporary hardness.

Detergents work in hard water because their calcium and magnesium salts are soluble in water, unlike those of soap. This prevents the formation of scum, allowing the detergent to produce lather.

Nitrogen makes up approximately 78% of the Earth's atmosphere, making it the most abundant gas. Oxygen follows at about 21%, with other gases present in much smaller quantities.

Heavy water, or deuterium oxide, is water in which the hydrogen atoms are replaced by deuterium, which is an isotope of hydrogen with one neutron.

Chlorination is the process of adding chlorine or chlorine compounds to water to kill bacteria and other pathogens, making it safe for drinking.

Fertilisers typically contain nitrogen, phosphorus, and potassium (NPK). Chlorine is not a primary nutrient added to fertilisers and can actually be harmful to some plants in high concentrations.

Paracetamol is an analgesic (pain reliever) and antipyretic (fever reducer). It is not an antibiotic, which is used to treat bacterial infections.

Sulphur dioxide (SO2) reacts with water to form sulphurous acid (H2SO3), which is a strong acid in aqueous solution. Ammonia forms a basic solution, and hydrogen sulphide is a very weak acid.

Sulphur dioxide is a common bleaching agent, particularly for delicate materials like wool and silk, as it acts as a reducing agent to remove color.

Rabies is caused by a virus, Leprosy is caused by bacteria (Mycobacterium leprae), and Malaria is caused by a protozoan (Plasmodium). Therefore, i-B, ii-A, iii-C is the correct match.

At night, photosynthesis stops, but plants continue to respire, consuming oxygen and releasing carbon dioxide. Therefore, sleeping under a tree at night can lead to higher concentrations of carbon dioxide.

Pure gold is defined as 24-carat gold. Lower carat values indicate that the gold has been alloyed with other metals to increase its strength.

Copper was the first metal to be widely used by humans, marking the beginning of the Copper Age, as it could be found in its native state and was relatively easy to work with.

River water is harder than rain water because it flows over rocks and soil, dissolving minerals like calcium and magnesium salts along the way. Rain water is essentially distilled water before it hits the ground.

Dialysis is a medical procedure used to perform the function of the kidneys for patients whose kidneys are failing, specifically to remove waste products and excess fluid from the blood.

Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In the case of sugar, yeast enzymes convert glucose into ethyl alcohol and carbon dioxide.

Hydrochloric acid is a strong acid, which means it completely dissociates in water to release a high concentration of hydrogen ions. A strong acid solution typically has a very low pH, usually between 0 and 2.

Sea water contains a high concentration of dissolved salts, the most abundant of which is sodium chloride, commonly known as common salt.

Ethylene and styrene are monomers containing carbon-carbon double bonds. These double bonds allow them to undergo addition polymerization to form long-chain polymers like polyethylene and polystyrene.

Isobars are atoms of different chemical elements that have the same mass number but different atomic numbers. This means they have a different number of protons but the same total number of nucleons.

Diamond is an allotrope of carbon, meaning it consists entirely of carbon atoms arranged in a specific crystal lattice structure. It is not a mixture or a compound of other elements.

Wrought iron is the purest form of commercial iron, containing the lowest percentage of carbon (typically less than 0.08 percent). In contrast, pig iron and cast iron have much higher carbon contents.