CHEMISTRY (Part-VIII) (Railway)

Total Questions: 50

31. Plaster of Paris should be stored in sealed containers. Which of the following is the correct explanation for the given assertion? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-I)]

(1) It turns into a hard solid after reacting with moisture present in air.
(2) It decomposes in the presence of sunlight.
(3) It turns into hard solid after reacting with oxygen present in the air.
(4) It decomposes in the presence of oxygen.

Correct Answer: (1) It turns into a hard solid after reacting with moisture present in air.

Solution:It turns into a hard solid after reacting with moisture present in air.
• The Plaster of Paris is calcium sulfate, and when the water of crystallisation is added to it, gypsum is formed, which is a hard material.
• CaSO₄·½H₂O + 3/2 H₂O → CaSO₄·2H₂O
• So, it should be stored in a waterproof container.

32. How many elements occur naturally? [RRB Group 'D' CBT Exam 20.09.2022 (Shift-I)]

(1) 93
(2) 95
(3) 94
(4) 92

Correct Answer: (2) 95

Solution:In the periodic table, there are 118 elements.
• Of these 118 elements, 94 occur naturally on Earth.
• Six of these occur in extreme trace quantities: technetium, promethium, astatine, francium, neptunium, and plutonium.

33. Which of the following statements regarding metals is NOT correct? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-I)]

(1) metals display electron losing tendency during bond formation
(2) Metals are placed towards the left in the periodic table.
(3) In general, metals form acidic oxides.
(4) Metals are electropositive in nature

Correct Answer: (3) In general, metals form acidic oxides.

Solution:Metals are those elements that tend to lose electrons. Non-metals are those elements that tend to gain electrons.
• Oxides of metals are basic in nature, whereas oxides of non-metals are acidic.
• Metal oxides on being dissolved in water release hydroxyl ions and are therefore basic.
• Non-metallic oxides on being dissolved in water release hydronium ions and are therefore acidic.

34. Select the functional group in five-carbon atom compound 'Pentanal'. [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-II)]

(1) Ketone
(2) Aldehyde
(3) Alcohol
(4) Alkene

Correct Answer: (2) Aldehyde

Solution:Pentanal (also called valeraldehyde) is a saturated fatty aldehyde composed from five carbons in a straight chain.

• It has the longest chain of five carbon and contains aldehyde (functional group).

35. Which of the following groups of elements were NOT discovered at the Mendeleev's periodic table? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-II)]

(1) Alkaline earth metals
(2) Noble gas
(3) Halogens
(4) Alkali metals

Correct Answer: (2) Noble gas

Solution:In the Mendeleev periodic table, there was no mention of noble gases like helium, neon, and argon krypton, xenon, and Radon.
• This was because they were not known at that time and were discovered much later.
• Since they are very inert gases, it was difficult to detect them with the primitive technology.

36. Baking soda is NOT generally used: [RRB Group 'D' CBT Exam. 20.09.2022 (Shift-II)]

(1) As a disinfectant
(2) as an antacid
(3) in fire extinguishers
(4) as baking powder

Correct Answer: (1) As a disinfectant

Solution:Sodium bicarbonate (NaHCO₃), also known as baking soda, is primarily used in cooking (baking) as a leavening agent.
• It reacts with acidic components in batters, releasing carbon dioxide, which forms the characteristic texture in pancakes, cakes, quick breads, etc.
• Bleaching powder or Calcium hypochlorite (Ca(OCl)₂) is used as disinfectant and germicide, especially in the sterilization of drinking water.

37. Which of the following structures is formed with a closed chain of carbon atoms? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-II)]

(1) Straight chain structure
(2) Branched chain structure
(3) Ring structure
(4) Acyclic structure

Correct Answer: (3) Ring structure

Solution:Catenation is a self-linking property which is found in carbon, by which it can combine with unlimited carbon atoms and can make different types of chain or ring structures.

• Due to catenation property, carbon leads to formation of straight chain, branch chain, and cyclic compounds.
• Example: Benzene has a ring-carbon chain structure.

38. Which of the following compounds is prepared when sodium chloride reacts with carbon dioxide in the presence of ammonia and water? [RRB Group 'D' CBT Exam. 20.09.2022 (Shift-II)]

(1) Na₂SO₄
(2) Na₂CO₃
(3) CaCO₃
(4) NaHCO₃

Correct Answer: (4) NaHCO₃

Solution:When a cold and concentrated solution of Sodium Chloride reacts with Carbon Dioxide and Ammonia, it forms Ammonium Chloride.

• NaCl + NH₃ + H₂O + CO₂ → NaHCO₃ + NH₄Cl
• Sodium Hydrogen Carbonate (NaHCO₃) is also called sodium bicarbonate or baking soda.

39. Which of the following are produced in a neutralisation reaction? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-II)]

(1) Acid and water
(2) Precipitate and base
(3) Salt and acid
(4) Salt and water

Correct Answer: (3) Salt and acid

Solution:A neutralisation reaction can be defined as a chemical reaction in which an acid and base quantitatively react together to form a salt and water as products.
• In a neutralization reaction, there is a combination of H⁺ ions and OH⁻ ions which form water.
• Example: HCl (Hydrochloric acid) + NaOH (Sodium Hydroxide) → NaCl (Sodium Chloride) + H₂O (Water)

40. Which of the following is reduced in the given reaction? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-II)]

ZnO + C → Zn + CO

(1) CO
(2) ZnO
(3) Carbon
(4) Zn

Correct Answer: (2) ZnO

Solution:Adding oxygen to material and removing hydrogen from a substance is known as an oxidation reaction.
• The addition of oxygen causes the oxidation of C to CO.
• Since oxygen is eliminated, ZnO is reduced to Zn.

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