Chemistry Questions and Answers

Answer: A

Only one type of solid has all three properties: Only one, the metallic solids.

In a metal, positive ions sit in a sea of delocalised electrons. The free electrons conduct electricity, and because the bonding is non-directional, layers of ions can slide over one another without breaking the solid, which makes metals malleable and ductile.

Ionic solids conduct only when molten or dissolved and are brittle. Covalent network solids such as diamond are hard and brittle (graphite conducts but is not malleable). Molecular solids are soft, low-melting insulators.

Answer: B

The correct statement is that alkaline batteries exhibit a gradual decrease in voltage output over time.

As an alkaline cell discharges, its voltage falls steadily from about 1.5 V. Lithium cells hold a much flatter voltage for most of their life and then drop off sharply near the end.

The other statements are reversed. Ordinary alkaline cells are primary cells, not designed to be recharged, so 'both generally rechargeable' is wrong. Lithium batteries have a higher energy density than alkaline batteries, which is why they are used in phones and laptops, and it is lithium, not alkaline, that keeps a consistent voltage.

Answer: A

The chemical is Silver iodide.

Silver iodide has a crystal structure very close to that of ice, so its particles act as nuclei on which supercooled water droplets in a cloud freeze into ice crystals. The crystals grow and fall, melting into rain on the way down. It is dispersed from aircraft or ground generators; dry ice and common salt are also used for seeding.

Magnesium nitrate and potassium permanganate have no such role, and diphenyl carbazide is a laboratory reagent used to detect chromium.

Answer: D

The incorrect statement is acetic and formic acids are the most common acids in apple.

The main acid in apples is malic acid (the name comes from malum, Latin for apple). Acetic acid is the acid of vinegar, and formic acid is found in ant stings and nettles.

The other statements are accepted. Baking soda (sodium bicarbonate) releases carbon dioxide and is used in dry-chemical and soda-acid fire extinguishers. Tooth enamel is made of calcium phosphate (hydroxyapatite), a basic compound, which is why acids erode it. Ascorbic acid (vitamin C) treats scurvy.

Answer: B

X is lithium.

Lithium is a soft, silvery-white alkali metal used in rechargeable batteries, which makes it a critical mineral for electric vehicles and energy storage. In 2023 the Geological Survey of India reported inferred lithium resources of about 5.9 million tonnes in the Salal-Haimana area of Reasi district, Jammu and Kashmir. Argentina, Bolivia and Chile form the 'lithium triangle', holding more than half of the world's resources.

Cesium is also an alkali metal but not the one in these news reports, while selenium is a non-metal and aluminium is not an alkali metal.

Answer: B

Only statement 2 is correct.

Graphite is soft and slippery because its hexagonal layers slide over one another, and it conducts electricity because each carbon has one free electron.

Statement 1 describes graphite, not diamond: in diamond each carbon is bonded to four others in a tetrahedral, three-dimensional network, which makes it so hard. Statement 3 is wrong on several counts: carbon is tetravalent, not trivalent, and its versatility comes from catenation, tetravalency and its small atomic size, which allows strong bonds.

Answer: B

The code is P Q T S.

W: iron is the second most abundant metal in the earth's crust, after aluminium (P).
X: aluminium is protected by a thin, tough layer of its own oxide, which stops further corrosion (Q).
Y: 'nila thotha' is blue vitriol, copper sulphate, \(CuSO_{4} \cdot 5H_{2}O\) (T).
Z: bronze is an alloy of copper and tin (S).

Zinc (R) belongs to none of these, so the codes that use it are wrong.

Answer: B

Diesel is a mixture of \(C_{15}H_{32}\) to \(C_{18}H_{38}\) hydrocarbons.

Diesel fuel is a middle distillate of petroleum boiling roughly between 200 and 350 degrees C, made up mostly of alkanes with about 12 to 20 carbon atoms. Of the ranges offered, \(C_{15}\) to \(C_{18}\) lies squarely within that band.

\(C_{5}\) to \(C_{10}\) compounds such as octane (\(C_{8}H_{18}\)) make up petrol (gasoline), which is lighter and more volatile, and \(C_{20}\) to \(C_{22}\) chains belong to heavier oils and waxes. Option C's \(C_{5}H_{14}\) is not even a possible alkane, since pentane is \(C_{5}H_{12}\).

Answer: B

The everyday effects of oxidation are corrosion and rancidity.

Corrosion is the slow oxidation of a metal by air and moisture, such as the rusting of iron or the green coating on copper. Rancidity is the oxidation of fats and oils in food, which gives it a bad smell and taste; it is slowed by antioxidants, airtight packing or flushing packets with nitrogen.

Decomposition and precipitation are other kinds of reaction, and malleability and ductility are physical properties of metals, not effects of oxidation.

Answer: B

The property is malleability.

Malleability is the ability of a metal to be hammered or rolled into thin sheets without breaking; gold, silver and aluminium are highly malleable.

Ductility is the ability to be drawn into wires, conductivity is the ability to conduct heat and electricity, and sonority is the ringing sound metals make when struck. Only malleability is about beating into sheets.