Here are 25 multiple-choice questions on Basic Chemistry for the JKSSB Forester exam, with answers and explanations:
Q1. Which of the following is an example of a physical change?
(a) Burning of wood
(b) Rusting of iron
(c) Dissolving sugar in water
(d) Digestion of food
Answer: (c)
Explanation: A physical change alters the form of a substance but not its chemical composition. Dissolving sugar in water changes its state and appearance, but sugar and water remain chemically the same. Burning, rusting, and digestion are chemical changes.
Q2. What is the SI unit of mass?
(a) Gram
(b) Pound
(c) Kilogram
(d) Milligram
Answer: (c)
Explanation: The SI (International System of Units) unit of mass is the kilogram (kg).
Q3. Which subatomic particle has a negative charge?
(a) Proton
(b) Neutron
(c) Electron
(d) Nucleon
Answer: (c)
Explanation: Electrons carry a negative charge, protons carry a positive charge, and neutrons have no charge (are neutral).
Q4. The atomic number of an element is determined by the number of:
(a) Neutrons
(b) Protons
(c) Electrons
(d) Protons and neutrons
Answer: (b)
Explanation: The atomic number (Z) of an element is uniquely defined by the number of protons in the nucleus of an atom of that element.
Q5. Which of the following is a noble gas?
(a) Oxygen
(b) Nitrogen
(c) Argon
(d) Chlorine
Answer: (c)
Explanation: Noble gases are elements in Group 18 of the periodic table, known for their low reactivity. Argon (Ar) is a noble gas. Oxygen, nitrogen, and chlorine are reactive non-metals.
Q6. What is the chemical symbol for sodium?
(a) So
(b) Na
(c) Sd
(d) Sn
Answer: (b)
Explanation: The chemical symbol for sodium is Na, derived from its Latin name “natrium”.
Q7. Which type of bond involves the sharing of electrons between atoms?
(a) Ionic bond
(b) Covalent bond
(c) Metallic bond
(d) Hydrogen bond
Answer: (b)
Explanation: A covalent bond is formed when two atoms share one or more pairs of electrons. Ionic bonds involve the transfer of electrons.
Q8. An acid is a substance that produces ______ ions when dissolved in water.
(a) OH$^{-}$
(b) H$^{+}$
(c) Cl$^{-}$
(d) Na$^{+}$
Answer: (b)
Explanation: According to the Arrhenius definition, an acid produces hydrogen ions (H$^{+}$) when dissolved in water, while a base produces hydroxide ions (OH$^{-}$).
Q9. What is the pH of a neutral solution at 25°C?
(a) 0
(b) 7
(c) 14
(d) 1
Answer: (b)
Explanation: A neutral solution, such as pure water, has a pH of 7 at 25°C. Acidic solutions have a pH less than 7, and basic solutions have a pH greater than 7.
Q10. Which famous scientist proposed the planetary model of the atom?
(a) J.J. Thomson
(b) Ernest Rutherford
(c) Niels Bohr
(d) John Dalton
Answer: (b)
Explanation: Ernest Rutherford’s gold foil experiment led to the proposal of the nuclear model (often called the planetary model) of the atom, where electrons orbit a central, dense nucleus.
Q11. The process of conversion of a solid directly into a gas without passing through the liquid state is called:
(a) Evaporation
(b) Condensation
(c) Sublimation
(d) Melting
Answer: (c)
Explanation: Sublimation is the process where a solid changes directly into a gas without becoming a liquid first (e.g., dry ice).
Q12. What is the principal component of natural gas?
(a) Ethane
(b) Propane
(c) Butane
(d) Methane
Answer: (d)
Explanation: Methane (CH$_{4}$) is the simplest hydrocarbon and the primary component of natural gas, typically making up 70-90% of its volume.
Q13. The general formula for alkanes is:
(a) C$_{n}$H$_{2n}$
(b) C$_{n}$H$_{2n-2}$
(c) C$_{n}$H$_{2n+2}$
(d) C$_{n}$H$_{n}$
Answer: (c)
Explanation: Alkanes are saturated hydrocarbons with only single bonds between carbon atoms. Their general formula is C$_{n}$H$_{2n+2}$, where ‘n’ is the number of carbon atoms.
Q14. Which of the following is commonly known as “laughing gas”?
(a) Nitric oxide (NO)
(b) Nitrous oxide (N$_{2}$O)
(c) Nitrogen dioxide (NO$_{2}$)
(d) Ammonia (NH$_{3}$)
Answer: (b)
Explanation: Nitrous oxide (N$_{2}$O) is commonly known as laughing gas due to its euphoric effects when inhaled.
Q15. The phenomenon by which an element exists in different physical forms is called:
(a) Isomerism
(b) Allotropy
(c) Isotopy
(d) Polymerization
Answer: (b)
Explanation: Allotropy is the property of some chemical elements to exist in two or more different forms (allotropes) in the same physical state (e.g., carbon exists as diamond, graphite, fullerene).
Q16. What is the chemical formula for water?
(a) H$_{2}$O$_{2}$
(b) CO$_{2}$
(c) H$_{2}$O
(d) CH$_{4}$
Answer: (c)
Explanation: The chemical formula for water is H$_{2}$O, indicating two hydrogen atoms bonded to one oxygen atom.
Q17. Which of these is a homogeneous mixture?
(a) Sand and water
(b) Oil and water
(c) Air
(d) Iron filings and sulfur
Answer: (c)
Explanation: A homogeneous mixture has a uniform composition throughout. Air is a mixture of gases (nitrogen, oxygen, etc.) that are evenly distributed. Sand and water, oil and water, and iron filings and sulfur are heterogeneous mixtures.
Q18. What is the primary function of a catalyst in a chemical reaction?
(a) To increase the activation energy
(b) To decrease the activation energy
(c) To shift the equilibrium position
(d) To consume reactants
Answer: (b)
Explanation: A catalyst speeds up a chemical reaction by providing an alternative reaction pathway with a lower activation energy, without being consumed in the overall reaction.
Q19. The process of adding a protective zinc coating to steel or iron to prevent rusting is known as:
(a) Electroplating
(b) Annealing
(c) Galvanization
(d) Hardening
Answer: (c)
Explanation: Galvanization is a common method of preventing corrosion by coating iron or steel with a thin layer of zinc.
Q20. Which element is essential for all organic compounds?
(a) Oxygen
(b) Nitrogen
(c) Carbon
(d) Hydrogen
Answer: (c)
Explanation: Organic chemistry is the study of carbon-containing compounds. Carbon’s ability to form stable bonds with itself and other elements makes it the backbone of all organic molecules.
Q21. The chemical reaction in which heat is released is called:
(a) Endothermic reaction
(b) Exothermic reaction
(c) Reversible reaction
(d) None of the above
Answer: (b)
Explanation: An exothermic reaction is a chemical reaction that releases energy by light or heat to its surroundings. An endothermic reaction absorbs energy.
Q22. What is the approximate percentage of nitrogen in the Earth’s atmosphere?
(a) 21%
(b) 78%
(c) 0.03%
(d) 1%
Answer: (b)
Explanation: Nitrogen (N$_{2}$) makes up approximately 78% of the Earth’s atmosphere, making it the most abundant gas.
Q23. Which of the following is a strong acid?
(a) Acetic acid (CH$_{3}$COOH)
(b) Hydrochloric acid (HCl)
(c) Carbonic acid (H$_{2}$CO$_{3}$)
(d) Citric acid (C$_{6}$H$_{8}$O$_{7}$)
Answer: (b)
Explanation: Strong acids completely dissociate in water, releasing all their H$^{+}$ ions. Hydrochloric acid (HCl) is a common strong acid. Acetic acid, carbonic acid, and citric acid are weak acids.
Q24. Isotopes are atoms of the same element that have:
(a) Different atomic numbers but same mass numbers
(b) Same atomic numbers but different mass numbers
(c) Same number of protons and electrons
(d) Different number of protons and neutrons
Answer: (b)
Explanation: Isotopes are variants of a particular chemical element that have the same number of protons (atomic number) but different numbers of neutrons, resulting in different mass numbers.
Q25. The phenomenon of radioactivity was discovered by:
(a) Marie Curie
(b) Ernest Rutherford
(c) Henri Becquerel
(d) Pierre Curie
Answer: (c)
Explanation: Henri Becquerel discovered radioactivity in 1896 when he observed that uranium salts emitted rays that could penetrate opaque materials. The Curies later did extensive work on the topic.
