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
41. Which of the following are the limitations of Bohr’s model of atom?
[A] it cannot explain spectrum of atoms containing more than one electron
[B] it cannot explain the Zeeman effect
[C] it cannot explain the Stark effect
[D] All of the above
Show Answer
Correct Answer: D [All of the above]
Notes:
Bohr’s model of atom cannot explain spectrum of atoms containing more than one electron. Also, it cannot explain the Zeeman effect i.e. splitting of spectral line in presence of magnetic field. It also fails to explain Stark effect i.e. splitting of spectral line in presence of electric field.
42. What is the general Q-value for alpha-decay?
[A] greater than 0
[B] less than 0
[C] equal to 0
[D] None of the above
Show Answer
Correct Answer: A [greater than 0]
Notes:
Q-value is the net kinetic energy gained in the process or, if the initial nucleus X is at rest, the kinetic energy of the products. Clearly, Q> 0 for exothermic processes such as α-decay.
43. What is the S.I unit of activity?
[A] becquerel
[B] curie
[C] candela
[D] henry
Show Answer
Correct Answer: A [becquerel]
Notes:
The SI unit for activity is becquerel, named after the discoverer of radioactivity, Henry Becquerel. The c.g.s unit of activity is curie.
44. Which of the following substance was used as a moderator in CIRUS reactor?
[A] Heavy water
[B] water
[C] solid graphite
[D] No moderator was used
Show Answer
Correct Answer: A [Heavy water]
Notes:
CIRUS (Canada India Research U.S.) reactor was constructed in 1960. This 40 MW reactor used natural uranium as fuel and heavy water as moderator.
45. What do we call the reactions in which there is an exchange of ions between the reactants?
[A] Double Displacement reaction
[B] Decomposition reaction
[C] Displacement reaction
[D] Combination reaction
Show Answer
Correct Answer: A [Double Displacement reaction]
Notes:
The reactions in which there is an exchange of ions between the reactants are called double displacement reactions.
46. Upto which element the Law of Octaves was found to be applicable?
[A] Carbon
[B] Calcium
[C] Iron
[D] Copper
Show Answer
Correct Answer: B [Calcium]
Notes:
It was found that the Law of Octaves was applicable only upto calcium. After calcium, every eighth element did not possess properties similar to that of the first element.
47. Which of the following is a part of chalcogen group of the modern periodic table?
[A] Boron
[B] Tin
[C] Lead
[D] Oxygen
Show Answer
Correct Answer: D [Oxygen]
Notes:
The chalcogens are the group 16 elements of the periodic table. This group is also known as the oxygen family. It consists of the elements oxygen (O), sulphur (S), selenium (Se), tellurium (Te), and the radioactive element polonium (Po).
48. Which of the following elements has the largest atomic radii?
[A] Lithium
[B] Beryllium
[C] Boron
[D] Carbon
Show Answer
Correct Answer: A [Lithium]
Notes:
The atomic radius generally decreases across a period. Therefore, Lithium will have the largest atomic radii among the given elements as it is placed before others as we move from left to right in the periodic table.
49. Choose the correct order in terms of Metallic character of these elements?
[A] Na> Mg >Be > P
[B] Mg >Be > P > Na
[C] Be> Mg > P > Na
[D] P> Be >Mg > Na
Show Answer
Correct Answer: A [Na> Mg >Be > P]
Notes:
The correct order would be Na> Mg >Be > P. Metallic character increases down a group and decreases along a period as we move from left to right.
50. What is the shape of XeF4 molecule?
[A] T-shaped
[B] Bent
[C] See-saw
[D] Square planar
Show Answer
Correct Answer: D [Square planar]
Notes:
The shape of XeF4 molecule is Square planar. As per VSEPR theory, there is repulsion between lone pair electrons and bond pair electrons as a result the Xenon tetrafluoride becomes square planar to achieve the stable state.
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