Chemistry (Part-XII)

41. Calcium Sulphate Dihydrate is commonly known as _____ . [S.S.C. Online Graduate Level (T-I) 3.03.2020 (Shift-III) ]

(a) asbestos
(b) limestone
(c) gypsum
(d) glass

Correct Answer: (c) gypsum

Solution:Calcium sulphate dihydrate (CaSO₄.2H₂O) is also called gypsum. It is heated to 393K to produce plaster of Paris (CaSO₄.1/2H₂O) which is used in the building industry as well as plaster for broken bones.

42. Due to which of the following reactions are household bleaching agents using phosphorous, sulphur and chlorine formed? [S.S.C. Online C.H.S.L. (T-I) 09.08.2021 (Shift-I) ]

(a) Decomposition reaction
(b) Disproportionation reaction
(c) Combination reaction
(d) Displacement reaction

Correct Answer: (b) Disproportionation reaction

Solution:While bleaching agents can involve various reactions, the formation of common household bleaching agents like sodium hypochlorite (

N a ClO

) often involves a disproportionation (or dismutation) reaction. In this type of redox reaction, a single element (like chlorine) is simultaneously oxidized and reduced.

43. Phosphorus is kept in water because- [S.S.C. Online Graduate Level (T-I) 1.09.2016 (Shift-I) ]

(a) its ignition temperature is very high
(b) its ignition temperature is very low
(c) its critical temperature is high
(d) its critical temperature is low

Correct Answer: (b) its ignition temperature is very low

Solution:White phosphorus is highly reactive and has a very low ignition temperature (around

3 0^{\circ} C

8 6^{\circ} F

). This means it can spontaneously ignite in air at room temperature. Storing it under water prevents it from coming into contact with oxygen, thus preventing combustion.

44. White phosphorus is stored in _____ . [S.S.C. Online MTS (T-I) 13.10.2017 (Shift-II) ]

(a) ether
(b) water
(c) mercury
(d) petrol

Correct Answer: (b) water

Solution:White phosphorous is a very flammable substance that is rapidly igniting in the air. It is insoluble in water. Therefore, white phosphorus is kept in water to avoid contact with air.

45. Which among the following is white phosphorus? [S.S.C. Online CHSL (T-I) 7.01.2017 (Shift-III) ]

(a) P₁
(b) P₆
(c) P₄
(d) P₅

Correct Answer: (c) P₄

Solution:White phosphorus exists as discrete tetrahedral

P₄

molecules. It's an allotrope of phosphorus that is very reactive and highly toxic. Other allotropes like red phosphorus and black phosphorus have different polymeric structures.

46. Which of the following gases are naturally formed via the anaerobic decay of phosphorus containing organic matter? [S.S.C. Online CGL (T-I) 24.08.2021 (Shift-III) ]

(a) Perchloryl fluoride
(b) Phosphine
(c) Phosgene
(d) Phosphorus pentafluoride

Correct Answer: (b) Phosphine

Solution:Phosphine (PH₃) or hydrogen phosphide gas is a toxic gas that results from the anaerobic decay of phosphorus-containing organic materials. It has an odor similar to that of garlic or decaying fish.

47. Which of the following is not a type of combination reaction? [S.S.C. Online MTS (T-I) 16.08.2019 (Shift-III) ]

(a) Adding of Water to Quick Lime
(b) Heating of Lime Stone
(c) Formation of water
(d) Burning of coal

Correct Answer: (b) Heating of Lime Stone

Solution:Heating limestone or calcium carbonate (CaCO₃) is a decomposition process. In this, carbon dioxide (CO₂) is liberated and calcium oxide (CaO) is formed.

48. Silver gets corroded due to _____ in air. [S.S.C. Online Graduate Level (T-I) 30.08.2016 (Shift-II) ]

(a) Oxygen
(b) Hydrogen Sulphide
(c) Carbon dioxide
(d) Nitrogen

Correct Answer: (b) Hydrogen Sulphide

Solution:The presence of hydrogen sulfide (H₂S) gas and other sulfur compounds in the air causes the sulfidation of silver, which reduces its luster. This is called the corrosion of silver.

49. Biofertilizers convert nitrogen to _____ . [S.S.C. Online Graduate Level (T-I) 30.08.2016 (Shift-II) ]

(a) Nitrates
(b) Ammonia
(c) Nitrogenase
(d) Amino Acids

Correct Answer: (b) Ammonia

Solution:Biofertilizers convert nitrogen to ammonia. This process, known as nitrogen fixation, is crucial for plant growth as it makes atmospheric nitrogen, which plants cannot directly utilize, available in a usable form.

50. Which of the following gas is present in biogas? [S.S.C. Online Stenographer 14.09.2017 (Shift-II) ]

(a) Ethane
(b) Methane
(c) Oxygen
(d) Nitrogen

Correct Answer: (b) Methane

Solution:Animals and plants are easily decomposed by anaerobic micro-organisms in the presence of wastewater. Gases like methane, carbon dioxide, hydrogen, hydrogen sulfide, ammonia, etc. are produced in this process. This mixture of gases is called biogas. A biogas plant is a unit that converts organic waste material (living biomass) into useful gaseous fuels (methane and carbon dioxide) and organic manure as a liquid as a by-product.