NCERT Class-9 Science Solutions: Chapter 4-Structure Of The Atom Part 2

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Question 7:

In the Thomson’s model of atom, which of the following statements are correct?

  1. The mass of the atom is assumed to be uniformaly distributed over the atom

  2. The positive charge is assumed to be uniformaly distributed over the atom

  3. The electrons are uniformaly distributed in the positively charged sphere

  4. The electrons attract each other to stabilise the atom

  5. (i), (ii) and (iii)

  6. (i) and (iii)

  7. (i) and (iv)

  8. (i), (iii) and (iv)

Answer: A

Image of Thomson's Model of the Atom

Image of Thomson's Model of the Atom

Image of Thomson's Model of the Atom

Question 8:

Rutherford’s α–particle scattering experiment showed that

  1. Electrons have negative charge

  2. The mass and positive charge of the atom is concentrated in the nucleus

  3. Neutron exists in the nucleus

  4. Most of the space in atom is empty

Which of the above statements are correct?

  1. (i) and (iii)

  2. (ii) and (iv)

  3. (i) and (iv)

  4. (iii) and (iv)

Answer: B

Question 9:

The ion of an element has 3 positive charges. Mass number of the atom is 27 and the number of neutrons is 14. What is the number of electrons in the ion?

  1. 13

  2. 10

  3. 14

  4. 16

Answer: B

Question 10:

Identify the ion from the Fig, where, represent the number of neutrons and protons respectively

Result for the number of neutrons and protons

The Number of Neutrons and Protons

Result for the number of neutrons and protons

Answer: D

Question 11:

In a sample of ethyl ethanoate the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

  1. One of the oxygen atoms has gained electrons

  2. One of the oxygen atoms has gained two neutrons

  3. The two oxygen atoms are isotopes

  4. The two oxygen atoms are isobars.

Answer: C