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Test: Structure Of The Atom- 1 - UPSC MCQ


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10 Questions MCQ Test Science & Technology for UPSC CSE - Test: Structure Of The Atom- 1

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Test: Structure Of The Atom- 1 - Question 1

Rutherford’s scattering experiment fails for very small scattering angles because

Detailed Solution for Test: Structure Of The Atom- 1 - Question 1

Rutherford's scattering formula fails for very small scattering angles because when the impact parameter is large compared to the size of the nucleus, alpha particles do not approach the nucleus closely. This invalidates Rutherford's assumption that alpha particles would come very close to the nucleus, leading to deviations from the expected scattering pattern predicted by his model. At larger distances (smaller scattering angles), interactions are weaker and dominated by screening effects from electrons, which Rutherford did not account for in his formula derived for close encounters.

Test: Structure Of The Atom- 1 - Question 2

Identify the Mg atom from the following figures where, n and p represent the number of neutrons and protons respectively.

Detailed Solution for Test: Structure Of The Atom- 1 - Question 2

Electronic configuration of 12Mg atom = 2, 8, 2 

Number of protons in Mg atom = 2+ 8 + 2 = 12

Number of neutrons in Mg atom = 24 -12 = 12
[as mass number of Mg atom = 24 and number of neutrons = mass number – number of protons]

Therefore, option (d) is the correct answer.

Test: Structure Of The Atom- 1 - Question 3

When alpha-particles are sent through a thin metal foil, most of them go straight through the foil because_______.

Detailed Solution for Test: Structure Of The Atom- 1 - Question 3

When alpha particles are sent through a thin metal foil, most of them go straight through the foil because most part of the atom is empty space. In other words, there is no obstruction in the path of alpha particles.

Test: Structure Of The Atom- 1 - Question 4

According to Bohr’s model, which of the following is true about electron orbits?

Detailed Solution for Test: Structure Of The Atom- 1 - Question 4

Neils Bohr proposed that electrons revolve around the nucleus only in specific allowed orbits called discrete orbits or energy levels.

Test: Structure Of The Atom- 1 - Question 5

Which of the following subatomic particles have no charge?

Detailed Solution for Test: Structure Of The Atom- 1 - Question 5

The subatomic particle with no charge is the neutron. Neutrons are one of the components of an atom's nucleus.

  • Neutrons have no electric charge.
  • They are found in the nucleus alongside protons, which have a positive charge.
  • Electrons, which orbit the nucleus, have a negative charge.
Test: Structure Of The Atom- 1 - Question 6

Rutherford’s a-particle scattering experiment showed that 
(i) electrons have negative charge 
(ii) the mass and positive charge of the atom is concentrated in the nucleus 
(iii) neutron exists in the nucleus 
(iv) most of the space in atom is empty 
Which of the above statements are correct?

Detailed Solution for Test: Structure Of The Atom- 1 - Question 6

Points (ii) and (iv) are correct. An atom consists of a positively charged, dense and very small nucleus which have all the protons and neutrons. Positive charge is due to protons, as neutrons have no charge. Most of the space is empty because most of the alpha particles pass straight through the gold foil without any deflection.
Electrons have negative charge, it was explained by Thomson. The existance of neutron was discovered by Chadwick.

Test: Structure Of The Atom- 1 - Question 7

The atomic number of an element is equal to:

Detailed Solution for Test: Structure Of The Atom- 1 - Question 7

The atomic number of an element is defined by: The number of protons in its nucleus. This number is crucial because: It determines the element's identity. It is equal to the number of electrons in a neutral atom.

Test: Structure Of The Atom- 1 - Question 8

Isotopes are atoms of the same element which have:

Detailed Solution for Test: Structure Of The Atom- 1 - Question 8

- Isotopes Definition: Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
- Atomic Number: This is the number of protons in an atom's nucleus, which defines the element.
- Mass Number: This is the total number of protons and neutrons in an atom's nucleus.
- Choice B describes isotopes accurately: they have different mass numbers due to varying neutrons, while their atomic number (protons) remains the same.

Test: Structure Of The Atom- 1 - Question 9

Isobars are atoms that have:

Detailed Solution for Test: Structure Of The Atom- 1 - Question 9

Isobars are defined by their mass numbers and atomic numbers.

  • Mass Numbers: Isobars have the same mass number.
  • Atomic Numbers: They possess different atomic numbers.

This means isobars are atoms with the same total number of protons and neutrons combined but differ in their number of protons (atomic number).

Test: Structure Of The Atom- 1 - Question 10

Which law states that "In a chemical substance, the elements are always present in definite proportions by mass"?

Detailed Solution for Test: Structure Of The Atom- 1 - Question 10

The Law of Definite Proportions is a fundamental principle in chemistry.

  • It states that in a chemical substance, the elements are always combined in the same proportions by mass.
  • This means the ratio of the masses of the elements in a compound is constant, no matter the source or amount of the compound.
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