Chemistry Questions and Answers

Answer: D

Bulletproof jackets are made with Kevlar.

Kevlar, an aramid (aromatic polyamide) fibre developed by Stephanie Kwolek at DuPont in 1965, is about five times stronger than steel by weight. Layers of Kevlar fabric absorb and spread the energy of a bullet, which is why it is used in body armour and helmets.

Nylon and Terylene (polyester) are synthetic fibres used in clothing, ropes and fabrics but are far too weak to stop bullets. Tweed is a woollen fabric.

Answer: C

The full forms are 1 and 4.

HMX (octogen) is a powerful high explosive, cyclotetramethylene tetranitramine. The letters are explained in two ways: 'High Melting Explosive', because it melts at a much higher temperature than its relative RDX, and 'Her Majesty's Explosive', from its British wartime development. Both are commonly given.

'High-Density Monoatomic Xenon' and 'Hedge Monetizing Xenocurrency' are invented and have nothing to do with HMX.

Answer: D

The key gives concentration of solution.

The concentration of a solution expresses how much solute is present in a given quantity of the solution or solvent, as in molarity (moles per litre of solution), molality (moles per kilogram of solvent) or mass percentage. Standard physical chemistry texts call this quantity the concentration of the solution.

'Concentration of solvent' reverses the roles of the components, and 'composition of solute' is not a term for this quantity. 'Concentration of solute' describes the same idea loosely, but the standard term, and the key, is concentration of solution.

Answer: B

The most useful basis is molecular targets.

Drugs can be classified by pharmacological effect (such as analgesics), by drug action on a biochemical process, by chemical structure, or by molecular target, the enzyme or receptor the drug binds to. As NCERT's chemistry textbook puts it, classification by molecular targets is the most useful one for medicinal chemists, because drugs acting on the same target tend to share structural features.

Pharmacological effect is useful to doctors, and chemical structure groups drugs that may act quite differently, so neither is the most useful for medicinal chemistry.

Answer: D

The answer is None of the above.

A catalyst, whether homogeneous (in the same phase as the reactants) or heterogeneous (in a different phase, such as a solid catalyst for gases), increases the rate of reaction by providing a path of lower activation energy. A promoter is a substance that increases the activity of a catalyst, as molybdenum does for iron in the Haber process.

Substances that slow a reaction are inhibitors (or poisons, for catalysts), and none is listed among the options, so 'None of the above' is correct.

Answer: C

The term is mole fraction.

The mole fraction of a component is the number of moles of that component divided by the total number of moles of all components in the solution:

\[ x_A = \frac{n_A}{n_A + n_B + \cdots} \]

Molarity is moles of solute per litre of solution, molality is moles of solute per kilogram of solvent, and mass percent is the mass of a component as a percentage of the solution's mass.

Answer: A

The key gives Composition.

Chemical properties describe how a substance's make-up changes in reactions, such as flammability or reactivity, and they are tied to its chemical composition. Composition can be determined only by changing the substance chemically, which is why it is grouped with chemical properties.

Melting point, odour and density are physical properties: they can be observed or measured without changing what the substance is made of.

Answer: B

The least reactive metal is gold.

In the reactivity series, metals are ranked by how readily they lose electrons. Calcium is near the top and reacts with cold water; zinc is in the middle and reacts with dilute acids; lead is lower and reacts only slowly. Gold is at the bottom: it does not react with water, air or ordinary acids, which is why it stays bright for centuries and is found free in nature.

The order of the four is calcium, zinc, lead, gold, from most to least reactive.

Answer: B

The term is molality.

Molality (m) is the number of moles of solute per kilogram of solvent:

\[ \begin{aligned} m &= \frac{n_{\text{solute}}}{w_{\text{solvent}}} \\ &\text{(mol per kg of solvent)} \end{aligned} \]

Because it uses mass rather than volume, molality does not change with temperature.

Molarity is moles of solute per litre of solution, mass percent is the mass of solute per 100 g of solution, and mole fraction is the moles of one component divided by the total moles of all components.

Answer: C

The reaction that is not feasible is Zn + \(\text{CaSO}_{4}\).

A metal displaces another from its salt solution only if it is more reactive. The reactivity series runs, from most to least reactive: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, copper. Zinc is less reactive than calcium, so it cannot displace calcium from calcium sulphate.

The others are possible on reactivity: iron is above lead, aluminium is above copper and magnesium is above zinc, so each of those metals can displace the less reactive metal from its sulphate.