CHEMISTRY (Part-VIII) (Railway)

Total Questions: 50

11. Which of the following compounds is used as a raw material for making plaster of Paris? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) Na₂CO₃ · 10H₂O
(2) CaSO₄ · 2H₂O
(3) CuSO₄ · 2H₂O
(4) MgSO₄ · 2H₂O

Correct Answer: (2) CaSO₄ · 2H₂O

Solution:Calcium sulfate dihydrate (CaSO₄·2H₂O) is used in the manufacture of Plaster of Paris.
Plaster of Paris is quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry.
It is produced by heating gypsum to about 150°C.

12. Which of the following is the correct balanced equation for the given chemical reaction? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

Fe + H₂O → Fe₃O₄ + H₂

(1) Fe(s) + 4H₂O(g) → 3Fe₃O₄(s) + H₂(g)
(2) 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)
(3) Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 2H₂(g)
(4) 3Fe(s) + H₂O(g) → 3Fe₃O₄(s) + H₂(g)

Correct Answer: (2) 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

Solution:The given equation is Fe + H₂O → Fe₃O₄ + H₂
On Reactant side, we have 1 Iron atom, 2 Hydrogen atoms, and 1 Oxygen atom.
On Product Side, we have 3 Iron atoms, 2 Hydrogen atoms, and 4 Oxygen atoms.

13. Metals are electropositive in nature. [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

Which of the following is the correct explanation for the given assertion?

(1) Metals gain electrons to form cations.
(2) Metals gain electrons to form anions.
(3) Metals lose electrons to form cations.
(4) Metals lose electrons to form anions.

Correct Answer: (3) Metals lose electrons to form cations.

Solution:Metals are electropositive in nature because all metals lose electrons from their outermost shell in order to become stable and hence become positively charged.
Non-metals are electronegative in nature because all non-metals gain electrons in order to become stable and hence become negatively charged.

14. Who among the following was first to find that every eighth element had properties similar to that of the first element? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) Dmitri Ivanovich Mendeleev
(2) Henry Moseley
(3) John Newlands
(4) Johann Wolfgang Döbereiner

Correct Answer: (3) John Newlands

Solution:In the year 1866, Newlands arranged the elements known at that time in an increasing order of their atomic masses.
He found that every eighth element had properties similar to those of the first.

15. Which of the following is the general formula of alkene? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) CₙH₂ₙ₊₄
(2) CₙH₂ₙ₋₂
(3) CₙH₂ₙ₂
(4) CₙH₂ₙ

Correct Answer: (4) CₙH₂ₙ

Solution:Alkenes (CₙH₂ₙ) are defined as either branched or unbranched hydrocarbons that possess at least one carbon-carbon double bond (CC).
• Because alkenes contain less than the maximum possible number of hydrogen atoms per carbon atom, they are said to be unsaturated.

16. Which of the following compounds reacts with carbon dioxide to form limestone? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) Calcium hydroxide
(2) Calcium oxide
(3) Calcium
(4) Calcium carbride

Correct Answer: (1) Calcium hydroxide

Solution:Calcium hydroxide (Ca(OH)₂) reacts with CO₂ to form salt calcium carbonate (CaCO₃) and water (H₂O).
The reaction is an example of a neutralisation reaction in which acid and base react with each other to form salt and water.
Calcium carbonate is also known as limestone.

17. What happens when concentrated hydrochloric acid is added to manganese dioxide? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) Hydrochloric acid is reduced to chlorine gas.
(2) Hydrogen gas is liberated.
(3) Manganese dioxide is reduced to manganese (II) chloride.
(4) Hydrochloric acid is reduced while MnO₂ is oxidised.

Correct Answer: (3) Manganese dioxide is reduced to manganese (II) chloride.

Solution:When the mixture of manganese dioxide and concentrated hydrochloric acid is subjected to heat, chlorine gas is liberated with formation of manganese chloride and water.
MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂
In this reaction, hydrochloric acid acts as a reducing agent and manganese dioxide acts as an oxidising agent.

18. Which of the following gases are evolved at the anode and the cathode, respectively, during electrolytic decomposition of aqueous sodium chloride? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) H₂ gas at the anode and O₂ gas at the cathode.
(2) O₂ gas at the anode and H₂ gas at the cathode.
(3) H₂ gas at the anode and Cl₂ gas at the cathode.
(4) Cl₂ gas at the anode and H₂ gas at the cathode.

Correct Answer: (4) Cl₂ gas at the anode and H₂ gas at the cathode.

Solution:Aqueous solution of sodium chloride is called brine.
• When electricity is passed through brine solution, the following reaction takes place:
• 2NaCl(aq) + 2H₂O(l) → Cl₂(g) + 2NaOH(aq) + H₂(g)
• Chlorine gas is given out at the anode and hydrogen gas given out at the cathode.
• he hydrogen gas burns a matchstick with a pop sound.

19. In the Modern Periodic Table, atomic size increases down the group because: [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) Tendency to lose electrons decreases
(2) Number of shells increases
(3) Valency increases
(4) Nuclear charge increases

Correct Answer: (2) Number of shells increases

Solution:On moving down the group in the periodic table, from top to bottom, the atomic size increases.
• This is because with increase in the atomic number, extra shells of electrons are added.
• These new shells take the outermost electrons farther from the nucleus, causing atomic size (radius) to increase as we go down the group.

20. 6CO₂(aq) + 12H₂O(I) → C₆H₁₂O₆(aq) + 6O₂(aq) + 6H₂O(I) [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

Select correct reaction conditions for the given reaction.

(1) Sunlight and chlorophyll
(2) High temperature
(3) Inert atmosphere
(4) High pressure

Correct Answer: (1) Sunlight and chlorophyll

Solution:Plants synthesize food directly from carbon dioxide and water using energy of light.

• In photosynthesis, chlorophyll in the leaves of plants absorbs light energy from the Sun.
• Plants use this energy to convert water and CO₂ from the environment into glucose and oxygen.

• 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

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