Railway Science (Chemistry-Chemical Reaction) (Part-VI)

Total Questions: 50

41. Magnesium ribbon burns with a dazzling white flame and changes into a ______coloured powder. [RRB Group D 15/10/2018 (Afternoon)]

Correct Answer: (a) white
Solution:

The burning of magnesium metal in air: 2Mg + O₂ → 2MgO + energy (heat). The Oxidation state of Mg changes from (0) in free state to (+2) in its oxide. Similarly the Oxidation state of O changes from 0 to (-2), getting reduced in the process. Since both oxidation and reduction occurs simultaneously, this is an example of Redox reaction.
Redox reaction - The reaction that involves the transfer of electrons from one species to another. The species that loses electrons is said to be oxidized and species that gains electrons is said to be reduced.

42. During a chemical reaction, the sum of the masses of reactants and products remains unchanged. What is this called? [RRB Group D 15/10/2018 (Evening)]

Correct Answer: (d) Principle of mass conservation
Solution:

Principle of mass conservation: This principle states that mass is conserved in a chemical reaction. It means that the total mass of the reactants is equal to the total mass of the products.

43. The decomposition reaction of plant matter into manure is an example of _______. [RRB Group D 15/10/2018 (Evening)]

Correct Answer: (a) exothermic
Solution:

Exothermic reaction. This reaction releases energy in the form of heat. Endothermic reaction: This reaction absorbs energy from the surroundings. Displacement reaction: This reaction involves one element replacing another in a compound.

44. Which of the following statements is true for metals? [RRB Group D 16/10/2018 (Evening)]

Correct Answer: (b) Metals have 1 to 4 valence electrons in their outermost shell.
Solution:

Noble gasses : 8 electrons in their outermost shell (Except- Helium). Metals have generally 1 to 3 valence electrons in their outermost orbit; some metals like tin (Sn) and lead (Pb) have 4 valence electrons. Non metals : They generally contain 4, 5, 6 or 7 electrons in the outermost shell and they ionise by gaining electrons.

45. Which of the following can undergo sublimation? [RRB Group D 16/10/2018 (Evening)]

Correct Answer: (a) Ammonium chloride
Solution:

Sublimation: This is the process where a solid changes directly into a gas without going through a liquid phase.

46. What happens when dilute hydrochloric acid is added to iron filings ? [RRB Group D 16/10/2018 (Evening)]

Correct Answer: (b) Hydrogen gas and iron chloride are produced
Solution:

Reaction: This is a single displacement reaction, where iron (Fe) displaces hydrogen (H) from the hydrochloric acid (HCl). The balanced chemical equation for this reaction is: Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g).

47. Combustion of coal and petroleum result in the formation of oxides of ______. [RRB Group D 22/10/2018 (Morning)]

Correct Answer: (c) 𝑁₂ and S
Solution:

This is because coal and petroleum fuels contain carbon, hydrogen, nitrogen, and sulfur as their main elements. When they are burned in the presence of oxygen, they produce carbon dioxide (CO₂), water (H₂O), nitrogen oxides (NOₓ), and sulfur oxides (SOₓ). Nitrogen oxides and sulfur oxides are harmful pollutants that can cause acid rain, smog, and respiratory problems.

48. The fumes of NO₂ are _______in colour. [RRB Group D 22/10/2018 (Afternoon)]

Correct Answer: (b) brown
Solution:

Nitrogen dioxide (NO₂) is responsible for the reddish-brown colour of smog. At high concentrations, NO₂ is highly toxic and can cause serious lung damage.

49. Pb + CuCl₂ → PbCl₂ + Cu. The given reaction is an example of a ______reaction. [RRB Group D 22/10/2018 (Afternoon)]

Correct Answer: (d) displacement
Solution:

Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and nonmetals take part in displacement reactions.

50. _________ is not a photochemical reaction. [RRB Group D 23/10/2018 (Morning)]

Correct Answer: (a) Synthesis of ammonia from nitrogen and hydrogen
Solution:

Synthesis of ammonia from nitrogen and hydrogen. A photochemical reaction is a chemical reaction that is initiated by light energy. Photosynthesis - A process in which green plants use sunlight to synthesize foods from carbon dioxide and water.