General Science Chemistry MCQs
Chemistry Objective (Multiple Choice) General Knowledge Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examination
31. What do the dots represent in the Lewis dot structures?
[A] positrons
[B] electrons
[C] atoms
[D] neutrons
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Correct Answer: B [electrons]
Notes:
The dots in the Lewis dot structure represent electrons. Lewis introduced theses simple notations to represent valence electrons in an atom.
32. What do we call the amount of energy required to break one mole of bonds of a particular type between two atoms in a gaseous state?
[A] Ionisation Potential
[B] Bond Enthalpy
[C] Electron affinity
[D] Bond order
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Correct Answer: B [Bond Enthalpy]
Notes:
Bond Enthalpy is the amount of energy required to break one mole of bonds of a particular type between two atoms in a gaseous state. Its unit is KJ-1.
33. What is meant by Bond length of two bonded atoms in a molecule?
[A] equilibrium distance between their valence electrons
[B] equilibrium distance between their outermost shell
[C] equilibrium distance between their nuclei
[D] twice the distance between their valence electrons
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Correct Answer: C [equilibrium distance between their nuclei]
Notes:
Bond length is defined as the equilibrium distance between the nuclei of two bonded atoms in a molecule.
34. Which of the following is correct about Ionic compounds?
[A] They have high melting and boiling points
[B] They are soluble in non-polar solvents
[C] They are usually gases in nature
[D] All of the above
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Correct Answer: A [They have high melting and boiling points]
Notes:
Ionic compounds have high melting and boiling points. They are soluble in polar solvents and are non-soluble in non-polar solvents. They are usually solids in nature.
35. What are the by-products of a hydrogen fuel cell?
[A] Water, heat and ozone
[B] Water and heat
[C] Water and ozone
[D] Heat, methane and Carbon dioxide
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Correct Answer: B [Water and heat]
Notes:
The only by-products in a fuel cell by combining hydrogen and oxygen are water and heat. They do not emit greenhouse gases or other air pollutants.
36. What percent of Carbon is present in the earth’s crust?
[A] 10%
[B] 76%
[C] 0.18%
[D] 38.2%
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Correct Answer: C [0.18%]
Notes:
Carbon is the 15th most abundant element in the earth’s crust with a percentage of 0.18%. Oxygen is the most abundant element at 46%, followed by silicon at 27% and aluminum at 8.1.
37. What do we call the compounds formed by the linking of carbon by single bonds in between them?
[A] Saturated compounds
[B] Unsaturated compounds
[C] Monovalent compounds
[D] Ionic compounds
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Correct Answer: A [Saturated compounds]
Notes:
The compounds formed by the linking of carbon by single bonds in between them are known as Saturated compounds. Alkanes are saturated compounds with Methane (CH4) being one of the simplest saturated compounds.
38. Which of these is a Thermoplastic polymer?
[A] Terylene
[B] Polythene
[C] PVC
[D] All of the above
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Correct Answer: D [All of the above]
Notes:
Thermoplastic polymers are linear polymers with very few cross linkages or no cross linkages at all. Polythene, PVC, polystyrene are addition type thermoplastics and Terylene, nylon are condensation type thermoplastics.
39. Which of these non-metals is lustrous?
[A] iodine
[B] selenium
[C] phosphorous
[D] All of the above
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Correct Answer: A [ iodine ]
Notes:
Iodine is the only non-metal which is lustrous in nature. All the other non-metals are non-lustrous in nature. This property of iodine makes it unique among the non-metals.
40. Which of the following is the method to get rid of temporary hardness of water?
[A] Boiling the water
[B] Addition of calcium hydroxide
[C] Both a and b
[D] None
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Correct Answer: C [Both a and b]
Notes:
The temporary hardness of water can be reduced either by boiling the water, or by the addition of lime (calcium hydroxide) through the process of lime softening.
