Chemistry Questions and Answers

Answer: B

The anaesthetic gas is nitrous oxide.

Nitrous oxide (N₂O), also called laughing gas because of the euphoria it causes, is widely used as a mild anaesthetic and painkiller in dentistry and surgery, usually mixed with oxygen.

Nitrogen dioxide (NO₂) is a toxic brown gas and a major air pollutant, nitric oxide (NO) is a colourless pollutant and signalling molecule in the body, and nitrogen (N₂) is the inert gas that makes up about 78% of air. None of them is used as an anaesthetic.

Answer: A

The most abundant metal in the earth's crust is aluminium.

Aluminium makes up about 8% of the crust by mass, more than any other metal. Overall, oxygen (about 46%) and silicon (about 28%) are the most abundant elements, followed by aluminium and then iron (about 5%).

Iron is the trap: it is the most abundant element in the earth as a whole, because the core is mostly iron, but in the crust it comes second among metals. Sodium is under 3% and manganese a small fraction of 1%.

Answer: B

The compound used in fire extinguishers is sodium bicarbonate.

Sodium bicarbonate (sodium hydrogencarbonate, NaHCO₃) releases carbon dioxide when it reacts with acid in a soda-acid extinguisher, or when it is heated in a dry-powder extinguisher. The carbon dioxide is heavier than air and blankets the fire, cutting off its oxygen.

Sodium carbonate (washing soda) is used for cleaning and making glass, sodium nitrate is a fertiliser and oxidising agent that can feed a fire, and sodium sulphate is used in detergents and paper making.

Answer: C

The oxide of aluminium is bauxite.

Bauxite is the main ore of aluminium and consists mostly of hydrated aluminium oxide (Al₂O₃ with water). It forms by intense weathering of rocks in hot, wet climates, much as laterite does, and India's large deposits are in Odisha, Jharkhand, Chhattisgarh and Gujarat. Aluminium is extracted from it by refining to alumina and then electrolysis.

Copper, zinc and manganese are separate metals, not compounds of aluminium at all, so none of them can be an oxide of it.

Answer: A

The major component is Copper sulphate.

Bordeaux mixture, one of the oldest fungicides, is made by mixing copper sulphate with lime (calcium hydroxide) in water. It was developed in France in the 1880s to control downy mildew on grapes and is still used against fungal diseases of crops.

Sodium chloride, calcium chloride and magnesium sulphate are not ingredients of the mixture.

It is sprayed as a protective fungicide on crops such as grapes, potatoes and fruit trees.

Answer: A

The gas is Ethylene.

Ethylene is a natural plant hormone that triggers ripening. Exposing mature green fruit such as bananas and mangoes to controlled amounts of ethylene gas in ripening chambers makes them ripen evenly and safely.

Ethane is a non-reactive hydrocarbon with no ripening effect, and carbon dioxide slows ripening rather than speeding it. Calcium carbide, which releases acetylene, is illegally used for ripening and is banned in India.

Answer: D

Alum purifies muddy water by Coagulation.

Mud particles in water are tiny colloidal particles carrying negative charges that keep them apart. Alum supplies aluminium ions with a high positive charge, which neutralise those charges, so the particles clump together, grow heavy and settle at the bottom.

Absorption, dialysis and emulsification are different processes; emulsification would keep particles dispersed rather than settling them.

Answer: A

The sweetest sugar is Fructose.

Fructose, the sugar of fruits and honey, is the sweetest natural sugar, about 1.7 times as sweet as sucrose (table sugar), which is taken as the standard of 1.

Glucose is less sweet than sucrose, at about three-quarters of its sweetness, and maltose (malt sugar) is much less sweet again, at roughly a third to a half of sucrose.

Answer: C

The one that is not an element is Marble.

An element is a substance made of only one kind of atom. Nitrogen, carbon and chlorine are elements. Marble is a metamorphic rock made mainly of calcium carbonate (CaCO₃), a compound of calcium, carbon and oxygen, so it is not an element. Marble forms when limestone is metamorphosed by heat and pressure.

The trap is carbon: marble contains carbon, but that does not make marble itself an element.

Answer: D

Pure gold is 24 carat.

Carat measures the purity of gold in twenty-fourths: 24 carat is pure gold (99.9 percent in practice). 22 carat is 22 parts gold in 24, about 91.6 percent, the usual standard for jewellery in India, since pure gold is too soft to hold its shape. In general, purity in percent is the carat value divided by 24 and multiplied by 100.

18 carat is 75 percent gold and 20 carat about 83 percent, so neither is pure.