Chemistry MCQs
Chemistry Objective (Multiple Choice) General Knowledge Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examination.
31. Element 106 was discovered by:
[A] Rutherford
[B] Seaborg
[C] Lawrence
[D] Kurchatove
Show Answer
Correct Answer: B [Seaborg]
Notes:
Element seaborgium (106) was discovered by Seaborg.
32. White phosphorus is generally kept under:
[A] Alcohol
[B] Water
[C] Glycerine
[D] Kerosene oil
Show Answer
Correct Answer: B [Water]
Notes:
White phosphorous is kept under water because it reacts with oxygen but not water. Besides, it is insoluble in water. It presents a significant fire hazard due to its extreme reactivity with atmospheric oxygen. It is also known to have very low ignition temperature to ignite/burn.
33. The most pure form of Carbon among the options is:
[A] Anthracite
[B] Lampblack
[C] Graphite
[D] Wood Charcoal
Show Answer
Correct Answer: C [Graphite]
Notes:
Wood charcoal and lamb black are the synthetically produced form of amorphous carbon. Between graphite and anthracite, graphite is a pure form of thermodynamically stable state of carbon. While the anthracite is the purest form of coal.
34. The manufacturing of iron from iron ore involves the process of:
[A] Oxidation
[B] Reduction
[C] Electrolysis
[D] Fractional distillation
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Correct Answer: B [Reduction]
Notes:Iron is extracted from iron ore in a huge container called a blast furnace. Iron ores such as hematite contain iron oxide. The oxygen must be removed from the iron oxide to leave the iron behind. Reactions in which oxygen is removed are called reduction reactions. Both carbon and carbon monoxide are used in the reduction of the iron oxide (Fe2O3) to give iron.
- 2Fe2O3 + 3C —> 4Fe + 3CO2
- CO2 + C —> 2CO.
- Fe2O3 + 3CO —> 2Fe + 3CO2
35. Bridgmanite is:
[A] A bridge on the river Thames
[B] Name of a game
[C] Earth’s most abundant mineral
[D] Name of a music
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Correct Answer: C [Earth’s most abundant mineral]
Notes:
Bridgmanite is the accepted name for the mineral silicate perovskite, (Mg,Fe)SiO3, the most common mineral on Earth. It was discovered in Tenham chondrite meteorite, where it associates with another polymorph of MgSiO3 substance – akimotoite.
36. Which of the following pairs is incorrect?
- Haematite : Iron
- Pitchblende : Copper
- Monazite : Thorium
Select the correct answer from the codes given below:
[A] Only 1
[B] Only 2
[C] Only 1 and 2
[D] Only 1 and 3
Show Answer
Correct Answer: B [Only 2]
Notes:
Pitchblende is a radioactive, uranium-rich mineral and ore. It has a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements. Commonly referred to as Uraninite, it is known as pitchblende due to its black color and high density.
37. Mass of a hydrogen atom is how many time the mass of an electron?
[A] 1000
[B] 8000
[C] 1837
[D] 5000
Show Answer
Correct Answer: C [1837]
Notes:
The mass of 1 hydrogen atom is estimated to be equal to the mass of a proton, which is equal to 1 AMU (Atomic Mass Unit). A hydrogen atom has only a proton in its nucleus. As the mass of an electron is 1/1837 times the mass of a proton (the mass of a proton is 1 AMU), therefore mass of a hydrogen atom is 1/1837 time the mass of an electron.
38. Which of the following gases has an odour that is similar to the odour of rotten eggs?
[A] Hydrogen Sulfide
[B] Dimethylcyclohexane
[C] Chlorine
[D] Ammonia
Show Answer
Correct Answer: A [Hydrogen Sulfide]
Notes:
Hydrogen sulfide (H2S) is a colourless gas with a characteristic odour of rotten eggs. It is often produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion.
39. Chemical formula of washing soda is:
[A] Na2SO4 .10H2O
[B] NaHCO3
[C] Na2CO3.10H2O
[D] Ca(OH)2
Show Answer
Correct Answer: C [Na2CO3.10H2O]
Notes:
Washing Soda is essentially Sodium Carbonate, a sodium salt of carbonic acid (soluble in water). The molecular formula of washing soda is Na2CO3.10H2O. It is used as an agent to soften hard water. Sodium ions present in it reacts with the calcium and magnesium ions replacing them to enable water, enabling the detergent to work.
40. Which method will be employed to test the hardness of water?
[A] Boiling
[B] Distillation
[C] Formation of lather with soap
[D] None of the above
Show Answer
Correct Answer: C [Formation of lather with soap]
Notes:
Soap solution is used to measure the hardness of rain water, temporarily hard water and sea-water. Hard water does not form lather with soap. This is because magnesium ions or calcium ions present in hard water react with soap to form calcium stearate or magnesium stearate forming water insoluble scum.
