General Knowledge (Part – B : english) (NDA/NA SOLVED PAPER 2021-I) (51 to 100)

Total Questions: 50

31. Which one of the following statements about the cleansing action of soap is not true?

Correct Answer: (c) Soaps are ammonium salts of long chain carboxylic acids.
Solution:Soap are sodium or potassium salts of long chain fatty acids.
  • Soap is a kind of molecule in which both the ends have different properties.
  • Hydrophilic end and Hydrophobic end
  • The first one is the hydrophilic end which dissolves water and is attracted to it whereas the second one is the hydrophobic end that is dissolved in hydrocarbons and is water repulsive in nature. If on the surface of the water, soap is present then the hydrophobic tail which is not soluble in water will align along the water surface.
  • The soap solution appears cloudy as it forms a colloidal solution which scatters light
  • Hard water contains calcium and magnesium ions, which react with the surfactant anion to give these metallic or lime soaps. In this reaction, the sodium cation in soap is replaced by calcium to form calcium stearate.

32. Hydrogenation of vegetable oils using nickel catalyst is an example of

Correct Answer: (c) Addition reaction.
Solution:Hydrogenation of oils in presence of palladium or nickel catalyst to form fat is an addition reaction. During hydrogenation, vegetable oils are reacted with hydrogen gas at about 60°C. A nickel catalyst is used to speed up the reaction. The double bonds are converted to single bonds in the reaction. In this way unsaturated fats can be made into saturated fats - they are hardened.

33. Which one of the following materials is not an allotrope of carbon ?

Correct Answer: (c) Fly ash
Solution:
  • When an element exists in more than one crystalline form, those forms are called allotropes.
  • The two most common allotropes of carbon are diamond and graphite.
  • Graphene is a two dimensional one atom thick allotrope of Carbon. Electrons in grapheme behave as massless relativistic particles. It is a 2 dimensional nanomaterial with many peculiar properties
  • Fly ash is not an allotrope of carbon.

34. Which one of the following reactions does not result in the evolution of hydrogen gas?

Correct Answer: (b) Mixing water to Plaster of Paris
Solution:
  • The chemical equation for the reaction of Plaster of Paris and water can be represented as CaSO₄. 1/2H₂O +3/2H₂O → CaSO₄ . 2H₂O.
    It does not produce hydrogen gas.
  • The reaction between zinc and sulphuric acid produces zinc sulphate and hydrogen gas. In the reaction, bubbles of hydrogen gas should be seen, and the zinc metal will dissolve to form aqueous zinc sulfate H₂SO₄ +Zn → H₂+ ZnSO₄
  • When sodium hydroxide solution is heated with zinc granules then Sodium zincate and hydrogen gas are formed. The salt formed by the reaction between a base and a metal, the metal is present as a part of the Negative ion. All the metals do not react with bases to form salt and hydrogen gas 2NaOH(aq)+Zn(s) → Na₂, ZnO₂, (aq) + H₂(g)
  • Potassium metal reacts very rapidly with water to form a colourless solution of potassium hydroxide (KOH) and hydrogen gas (H₂). The resulting solution is basic because of the dissolved hydroxide. The reaction is exothermic.

35. Which one of the following acids is predominantly found in tomatoes ?

Correct Answer: (c) Oxalic acid
Solution:Tomatoes contain oxdic acid predominantly.

36. Which one of the following conclusions could not be derived from Rutherford's α-particle scattering experiment?

Correct Answer: (c) Electrons move in a circular path of fixed energy called orbits.
Solution:Conclusion of Rutherford's scattering experiment:
  • Most of the space inside the atom is empty because most of the a-particles passed through the gold foil without getting deflected.
  • Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.
  • A very small fraction of α-particles were deflected by very large angles, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.
  • From the data he also calculated that the radius of the nucleus is about 10⁵ times less than the radius of the atom.

37. Reaction of quick lime (CaO) with water to produce slaked lime (Ca(OH)₂) is an example of

Correct Answer: (d) Exothermic reaction.
Solution:
  • An exothermic reaction is a reaction in which energy is released in the form of light or heat.
  • When quicklime is added to water, it forms slaked lime along with the evolution of heat. There will bea rise in the temperature of the bucket. Calcium oxide reacts with water to form calcium hydroxide, also called slaked lime.
  • CaO+H₂O→ Ca(OH)₂,

38. Which one of the following is not a bio-mass energy source?

Correct Answer: (b) Nuclear reactor
Solution:
  • Biomass is a clean, renewable energy source. Its initial energy comes from the sun, and plants or algae biomass can regrow in a relatively short amount of time. Trees, crops, and municipal solid waste are consistently available and can be managed sustainably.
  • Nuclear Reactor is not as source of biomaas energy.

39. Twinkling of stars is due to

Correct Answer: (c) atmospheric refraction of starlight.
Solution:
  • The twinkling of a star is due to atmospheric refraction of starlight. The starlight, on entering the earth's atmosphere, undergoes refraction continuously before it reaches the earth.
  • As light from a star races through our atmosphere, it bounces and bumps through the different layers, bending the light before you see it. Since the hot and cold layers of air keep moving, the bending of the light changes too, which causes the star's appearance to wobble or twinkle.

40. Which one of the following cannot be the unit of frequency of a sound wave?

Correct Answer: (a) dB
Solution:The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point per unit time.
Unit of frequently is S⁻¹ or min⁻¹ or Hz.
db or decibel is the unit of loudness of sound.