SOLVED PAPER 2020 (CDS) (I) (General Studies)

Total Questions: 120

1. Scattering of α-particles by a thin gold foil suggests the presence of

Correct Answer: (c) positively charged nucleus at the centre of an atom
Solution:Rutherford proposed the model which was based upon theα-particle scattering experiment. In this experiment, Rutherford concluded that the atom consists of a heavy and positively charged part at its centre, called the nucleus. The entire mass of an atom resides in its nucleus and is equal to the sum of masses of protons and neutrons, since the mass of electron is negligible.

2. The elements of which of the following pairs are isobars?

Correct Answer: (d)
Solution:Isobars are the atoms of different elements that have same mass number but different atomic number. Therefore, the elements of ⁴⁰Ar₁₈ and ⁴⁰Ca₂₀ are isobars.

3. Which one of the following chemical reaction is not feasible?

Correct Answer: (c) Cu + PbCl₂ → CuCl₂ + Pb
Solution:
  • Fe + CuSO₄ → FeSO₄ + Cu
    In this reaction, iron being more reactive than Cu, displaces Cu from CuSO₄ solution and forms new product, iron sulphate and Cu metal. So, this reaction is feasible.
  • Zn + CuSO₄ → ZnSO₄ + Cu
    In this reaction, zinc being more reactive than Cu, displaces Cu from. CuSO₄ solution and forms zinc sulphate and Cu metal. So, this reaction is also feasible.
  • Cu + PbCl₂ → CuCl₂ + Pb
  • This reaction is not feasible because lead chloride (PbCl₂) is less soluble. Thus, in this reaction, Pb not displaced by PbCl₂.
  • Mg + CuSO₄ → MgSO₄ + Cu
    In this reaction, magnesium is more reactive than Cu. It displaces Cu from CuSO₄ solution and form magnesium sulphate and Cu metal. Hence, this reaction is feasible.

4. A solution having pH equal to zero is known as

Correct Answer: (b) Highly acidic solution
Solution:pH is a number which indicates the acidic or basic nature of a solution. The solutions having pH between 0 to 2 are strongly acidic, those with pH between 2 to 4 are moderately acidic, while others having pH between 4 to 7 are weakly acidic. When the solutions having pH equal to 7 are neutral whereas others which have pH between 12 to 14 are strongly alkaline.

5. Which one of the following acids is produced in human stomach?

Correct Answer: (d) Hydrochloric acid
Solution:Stomach acid or gastric juice, is a digestive acid i.e., formed in the stomach and is composed of hydrochloric acid (HCl), potassium chloride (KCl) and sodium chloride (NaCl). Hydrochloric acid (HCl) plays a key role in digestion of proteins and enzymes.

6. Match List-I with List-II and select the correct answer using the codes given below the Lists

List-I (Compound)List-II (Use)
(A) Boric acid1. Antiseptic
(B) Citric acid2. Food preservative
(C) Magnesium hydroxide3. Antacid
(D) Acetic acid4. Pickle
Code:ABCD
(a)1234
(b)1324
(c)4321
(d)4231
Correct Answer: (a)
Solution:Boric acid is used as an antiseptic and insecticide.
  • Citric acid is used as a preservative and flavouring agent in food and beverages such as soft drinks.
  • Magnesium hydroxide reduces stomach acid, hence it is used as an antacid.
  • Acetic acid is used in pickle as Vinegar. Thus, the correct code is given in option (a).

7. The property of the sound waves that determines the pitch of the sound is its

Correct Answer: (a) frequency
Solution:The property of the sound waves that determines the pitch of the sound is its frequency. The pitch of a sound depends on the frequency of vibration. Greater the frequency of a sound, the higher will be its pitch.

8. Which one of the following is not a property of the X-rays?

Correct Answer: (a) They are deflected by electric fields.
Solution:X-rays are not deflected by electric fields because X-rays do not carry any charge. These waves are electromagnetic radiations. X-rays were discovered by Roentgen in 1895. Their wavelength is of the order of 10−12m to 10−8m. They are mainly used in detecting the fracture of bones, hidden bullet, needle, costly material etc, inside the body and also used in the study of crystal structure.

Properties of X-rays are :

  • They are not deflected by electric and magnetic fields.
  • They have high penetration length in matter.
  • Their wavelength is much smaller than that of visible light.

9. Which one of the following is not true about the image formed by a plane mirror?

Correct Answer: (c) It is real image.
Solution:Image formed by a plane mirror has following properties :
  • It is always virtual and erect.
  • The size of image is equal to the size of the object.
  • The image formed is as far behind the mirror as the object is in front of it.
  • The image is laterally inverted (i.e., left seems to be right and vice-versa)

10. In a periscope, the two plane mirrors are kept

Correct Answer: (a) parallel to each other
Solution:In a periscope, the two plane mirrors are kept parallel to each other at an 45° angle with its surface, which helps to reflect the light rays from the upper end of the periscope to lower end of the periscope. Periscope is especially used in a submarine to see above the surface of the sea.