PMS 2026 GK Practice Set - 1000 One-Liners, Q101-150 (Chemistry: Atoms, Bonding, Radioactivity, Acids & Bases, Reactions) Solved MCQs

Correct Answer: Matter

An atom is the smallest unit of matter that retains the properties of an element.

Correct Answer: Protons & Neutrons

The nucleus of an atom contains protons and neutrons; electrons move around it.

Correct Answer: Orbitals / Energy levels

Electrons occupy energy levels (shells, described in the modern model as orbitals) around the nucleus.

Correct Answer: Number of protons

The atomic number of an element is the number of protons in the nucleus of its atoms.

Correct Answer: Protons + Neutrons

The mass number is the total number of protons and neutrons in the nucleus.

Correct Answer: Protons

Isotopes of an element have the same number of protons (same atomic number) but different numbers of neutrons.

Correct Answer: Neutrons

Isotopes differ in their number of neutrons, which gives them different mass numbers.

Correct Answer: Gain or loss of electrons

An ion is an atom (or group of atoms) that has gained or lost electrons and so carries a charge.

Correct Answer: Positively charged ion

A cation is a positively charged ion, formed when an atom loses electrons.

Correct Answer: Negatively charged ion

An anion is a negatively charged ion, formed when an atom gains electrons.

Correct Answer: Sharing of electrons

A covalent bond involves the sharing of electron pairs between atoms.

Correct Answer: Transfer of electrons

An ionic bond involves the transfer of electrons from one atom to another, forming oppositely charged ions.

Correct Answer: Metals

A metallic bond is the attraction between metal cations and the shared sea of electrons in a metal.

Correct Answer: Weak bond between molecules

A hydrogen bond is a weak attraction between molecules, involving a hydrogen atom bonded to a highly electronegative atom.

Correct Answer: Combining capacity

Valency indicates the combining capacity of an atom, i.e. how many bonds it can form.

Correct Answer: Two or more atoms chemically bonded

A molecule is two or more atoms chemically bonded together.

Correct Answer: 6.022 x 10^23

Avogadro's number is approximately 6.022 x 10^23, the number of particles in one mole.

Correct Answer: Carbon-12 atom

The atomic mass unit is defined with reference to the carbon-12 atom (1 amu = 1/12 the mass of a carbon-12 atom).

Correct Answer: Henri Becquerel

Radioactivity was discovered by Henri Becquerel in 1896, in his work on uranium salts.

Correct Answer: 2 protons & 2 neutrons

An alpha particle consists of 2 protons and 2 neutrons, i.e. a helium-4 nucleus.

Correct Answer: Electron or positron emitted from nucleus

A beta particle is an electron (or, in beta-plus decay, a positron) emitted from the nucleus.

Correct Answer: Electromagnetic wave / high-energy photon

Gamma radiation is electromagnetic radiation of very high energy, i.e. high-energy photons.

Correct Answer: Time for half of nuclei to decay

The half-life of a radioactive substance is the time taken for half of its nuclei to decay.

Correct Answer: Becquerel (Bq)

The SI unit of radioactivity is the becquerel (Bq), one disintegration per second.

Correct Answer: High conductivity & malleability

Metals generally have high electrical and thermal conductivity and are malleable.

Correct Answer: Poor conductors

Non-metals are generally poor conductors of heat and electricity (graphite is the well-known exception).

Correct Answer: Two or more metals

An alloy is a mixture of two or more metals, or of a metal with another element.

Correct Answer: Iron & Carbon

Steel is an alloy of iron and carbon (usually with small amounts of other elements).

Correct Answer: Copper & Zinc

Brass is an alloy of copper and zinc.

Correct Answer: Liquid metal at room temperature

Mercury is unique among metals in being a liquid at room temperature.

Correct Answer: Covalent compound

Water is a covalent compound: its hydrogen and oxygen atoms share electrons.

Correct Answer: Ionic compound

Common salt (sodium chloride) is an ionic compound formed by electron transfer between sodium and chlorine.

Correct Answer: HCl, H2SO4

Common acids include hydrochloric acid (HCl) and sulphuric acid (H2SO4).

Correct Answer: NaOH, KOH

Common bases include sodium hydroxide (NaOH) and potassium hydroxide (KOH).

Correct Answer: Acidity or alkalinity

The pH scale measures how acidic or alkaline a solution is (below 7 acidic, 7 neutral, above 7 alkaline).

Correct Answer: 7

A neutral solution has a pH value of 7 at standard conditions.

Correct Answer: Rearrangement of atoms

A chemical reaction involves the rearrangement of atoms as bonds break and form; atoms themselves are not created or destroyed.

Correct Answer: Heat

An exothermic reaction releases heat to its surroundings.

Correct Answer: Heat

An endothermic reaction absorbs heat from its surroundings.

Correct Answer: Loss of electrons

Oxidation is the loss of electrons by an atom, ion or molecule.

Correct Answer: Gain of electrons

Reduction is the gain of electrons by an atom, ion or molecule.

Correct Answer: Lowering activation energy

A catalyst increases the reaction rate by providing a pathway with lower activation energy, without being consumed.

Correct Answer: Using electricity to cause chemical change

Electrolysis involves using electric current to bring about a chemical change.

Correct Answer: Material with conductivity between conductor & insulator

A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator.

Correct Answer: Light energy into electricity

A photovoltaic (solar) cell converts light energy directly into electrical energy.

Correct Answer: Communication / broadcasting

Radio waves are used for communication and broadcasting.

Correct Answer: Medical imaging

X-rays are used for medical imaging (and in industry for inspecting materials).

Correct Answer: Cancer treatment & sterilization

Gamma rays are used in cancer treatment (radiotherapy) and in sterilizing medical equipment.