Chemistry MCQs
Chemistry Objective (Multiple Choice) General Knowledge Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examination.
1. According to Avogadro’s hypothesis, equal volumes of gases contain equal number of?
[A] Atoms
[B] Molecules
[C] Particles
[D] Electrons
Show Answer
Correct Answer: B [Molecules]
Notes:
Avogadro’s hypothesis was proposed by Amedeo Avogadro in 1811. It states that equal volumes of all gases, at the same temperature and pressure, contain equal numbers of molecules. Avogadro’s number is defined as 6.022×10^23 molecules per mole. This hypothesis was crucial for determining molecular weights and led to the development of the ideal gas law.
2. Which among the following will undergo a chemical reaction depending on the pH of the solution?
[A] Calcium Oxide
[B] Zinc Oxide
[C] Ferric Oxide
[D] Ferrous Oxide
Show Answer
Correct Answer: B [Zinc Oxide]
Notes:
Zinc oxide (ZnO) can undergo a chemical reaction depending on the pH of the solution. In acidic conditions, it can react to form zinc ions (Zn²⁺), while in alkaline conditions, it can form zincates. This behavior is due to its amphoteric nature, which allows it to react with both acids and bases. In contrast, calcium oxide (CaO) is basic, ferric oxide (Fe₂O₃) is generally inert in neutral pH, and ferrous oxide (FeO) is less reactive in varying pH levels.
3. Which among the following gives hissing sound when dissolved into H2O?
[A] CaCO2
[B] Ca(OH)2
[C] CaO
[D] CaCl2
Show Answer
Correct Answer: C [CaO]
Notes:
The correct answer is CaO (calcium oxide), which is also known as quicklime. When CaO is dissolved in water, it reacts exothermically to form calcium hydroxide (Ca(OH)2), producing a hissing sound due to the rapid release of heat and steam. This reaction is a classic example of a vigorous exothermic reaction in chemistry. Calcium oxide is commonly used in construction and as a drying agent.
4. How does the Isotope of Iodine, Iodine-135 plays an important role in Nuclear Power Generation?
[A] It is used as a fuel supplement in some of the modern Nuclear Reactors
[B] It is a bi-product of Nuclear Reaction which kills the neutrons and this inhibits the power formation
[C] It is a moderator used actively in the Nuclear Reactors
[D] It is an experimental substance for Nuclear Fusion
Show Answer
Correct Answer: B [It is a bi-product of Nuclear Reaction which kills the neutrons and this inhibits the power formation]
Notes:
Iodine-135 is a important by-product of nuclear fission, particularly in reactors using uranium fuel. It has a high neutron capture cross-section, meaning it effectively absorbs neutrons, which can inhibit the fission process and reduce reactor power output. This property makes it crucial for managing reactor control and safety, as its presence can lead to a phenomenon known as “neutron poison,” affecting the overall efficiency of the nuclear reaction.
5. Which among the following alkane has largely replaced the ozone layer-depleting halomethanes in household refrigerators and freezers?
[A] Methane
[B] Propane
[C] Butane
[D] Ethane
Show Answer
Correct Answer: C [Butane]
Notes:
Isobutane, which is known in the industry as R600A has been used in several domestic refrigerators in recent times because it is an excellent refrigerant and non-ozone depleting substance with low global warming potential. The only drawback is that it is highly inflammable.
6. Which among the following is the correct impact of the London Forces in the Cycloalkanes?
[A] The melting and boiling points get increased
[B] The Melting and boiling points get decreased
[C] There is not impact on the melting and boiling points
[D] The melting point increases but boiling point decreases
Show Answer
Correct Answer: A [The melting and boiling points get increased]
Notes:
Please note that the Cycloalkanes with more than 20 carbon atoms are called Cycloparaffins. The cycloalkanes have the same properties as the alkanes but they have `Higher Boiling & Melting points`. This is because of the stronger dispersion forces between the atoms known as London Forces.
7. Which among the following acids is generally used as a first hand test to judge whether a metal is Gold or not?
[A] Sulfuric Acid
[B] Nitric Acid
[C] Hydrochloric Acid
[D] Sulfurous Acid
Show Answer
Correct Answer: B [Nitric Acid]
Notes:
The funda is that when a small drop of a strong acid, such as nitric acid, is put onto the metal’s surface, most metals fizz or bubble, whilst precious metals (Gold or Platinum not silver) are unaffected.
8. What happens to the non-metallic character of elements in the p-block of the periodic table?
[A] non-metallic character decreases down the group
[B] non-metallic character increases down the group
[C] No fix pattern
[D] None
Show Answer
Correct Answer: A [non-metallic character decreases down the group]
Notes:
The non-metallic character of elements decreases down the group. In fact, the heaviest element in each p-block group is the most metallic in nature.
9. Which of the following represents the general formula for alkanes?
[A] CnH2n
[B] CnH2n-2
[C] CnH2n+2
[D] CnHn
Show Answer
Correct Answer: C [CnH2n+2]
Notes:
Alkanes are saturated open chain hydrocarbons containing carbon – carbon single bonds.
10. What is the hemihydrate of calcium sulphate commonly known as?
[A] Gypsum
[B] Plaster of Paris
[C] Chloroform
[D] Limestone
Show Answer
Correct Answer: B [Plaster of Paris]
Notes:
Plaster of Paris is the common name of calcium sulphate hemihydrate because half molecule of water is attached with calcium sulphate. The chemical formula of plaster of Paris is CaSO4.1/2H2O.
