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
21. Which of the following refining methods works on the principle that impurities are more soluble in the melt than in the solid state of the metal?
[A] Liquation
[B] Electrolytic refining
[C] Zone refining
[D] Vapour Phase refining
Show Answer
Correct Answer: C [Zone refining]
Notes:
Zone refining works on the principle that impurities are more soluble in the melt than in the solid state of the metal. This method is very useful for producing semiconductors.
22. 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.
23. Which of the following reactions take place when iron nail in a copper sulphate solution becomes brownish in colour?
[A] Decomposition reaction
[B] Displacement reaction
[C] Double Displacement reaction
[D] None of the above
Show Answer
Correct Answer: B [Displacement reaction]
Notes:
Iron nail in the Copper Sulphate solution become brownish in colour and the blue colour of copper sulphate solution fade. This happens because iron has displaced or removed another element, copper, from copper sulphate solution. This reaction is known as displacement reaction.
24. Which of these methods can be used to prevent rancidity?
[A] Adding antioxidants to the food
[B] Storing food at low temperature
[C] Replace the air with nitrogen in the packing material
[D] All of the above
Show Answer
Correct Answer: D [All of the above]
Notes:
When food containing fats and oils are exposed to the atmosphere, the oxidation of fat and oil occurs, this is called as Rancidity.
25. What is the relationship between half-life period and initial concentration of the reacting species for a first order reaction?
[A] Both are directly proportional to each other
[B] Both are inversely proportional to each other
[C] Both are independent of each other
[D] The half life is twice the concentration of reacting species
Show Answer
Correct Answer: C [Both are independent of each other]
Notes:
For a first order reaction, half-life period is constant, i.e., it is independent of initial concentration of the reacting species. for a zero order reaction, it is directly proportional to the initial concentration of the reactants and inversely proportional to the rate constant. .
26. Which of the following is correct about Mendeleev’s Periodic Table?
[A] Argon is placed before Potassium
[B] Cobalt is placed before Nickel
[C] Tellurium is placed before iodine
[D] All of the above
Show Answer
Correct Answer: D [All of the above]
Notes:
All statements represent the anomalous pairs of elements in Mendeleev’s Periodic Table. The atomic mass of argon is 39.9 and that of potassium 39.1. But argon is placed before potassium in the periodic table. Similarly, Tellurium is placed before iodine and Cobalt is placed before Nickel.
27. Choose the correct statement about d-block elements:
[A] These are the elements of Group 3 to 10
[B] All of them are metals
[C] Both a and b
[D] None
Show Answer
Correct Answer: B [All of them are metals]
Notes:
d-block elements are the elements of Group 3 to 12 in the centre of the Periodic Table. All of them are metals. These are characterised by the filling of inner d orbitals by electrons.
28. Choose the correct statement:
[A] Water exists as liquid due to hydrogen bonding
[B] Hydrogen bond is a weak bond as compared to ionic bond
[C] Both a and b
[D] None of the above
Show Answer
Correct Answer: C [Both a and b]
Notes:
Hydrogen bond is a weak bond and is quite small as compared to the covalent bond. it is due to hydrogen bonding only that water exists as a liquid.
29. In which of the following pairs is the repulsion greatest as per the VSEPR Theory?
[A] lone pair – lone pair
[B] lone pair – bond pair
[C] bond pair – bond pair
[D] Same for all
Show Answer
Correct Answer: A [lone pair – lone pair]
Notes:
The repulsion of a lone pair of electrons for another lone pair is greater than that between a bond pair and a lone pair which in turn is greater than that between two bond pairs. The correct order of repulsive force is as: lone pair – lone pair > lone pair – bond pair > bond pair – bond pair.
30. What is the bond angle in case of Ammonia molecule?
[A] 120°
[B] 150°
[C] 66°
[D] 107°
Show Answer
Correct Answer: D [107°]
Notes:
The bond angle in case of Ammonia molecule is 107° and the molecular geometry is trigonal pyramidal. The number of bond pairs in Ammonia is 3 and lone pair is 1.
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