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NCERT Exemplar · Class 9 · Science

Chapter 4: Structure of the Atom

Practice each question, then open the answer or worked solution.

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Multiple Choice Questions

18 questions
Q11Multiple choice

In a sample of ethyl ethanoate (\[C{H_3}COO{C_2}{H_5}\]), 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?

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Correct option: C
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Worked solution

Ans: (c) The two oxygen atoms are isotopes.

Explanation: Isotopes are atoms of the same element (with same atomic number) with different mass numbers. The difference in mass number is because of the different number of neutrons present in the atoms.


Q12Multiple choice

Elements with valency 1 are:

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Correct option: C
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Worked solution

Ans: (c) either metals or non-metals.

Explanation: If an element shows positive valency (like sodium), it is a metal; otherwise (negative valency like chlorine) it is a non-metal.


Q13Multiple choice

The first model of an atom was given by:

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Correct option: D
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Worked solution

Ans: (d) J.J. Thomson


Q14Multiple choice

An atom with 3 protons and 4 neutrons will have a valency of:

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Correct option: C
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Worked solution

Ans: (c) 1

Explanation: Electronic configuration of this element will be 2, 1 (Atomic number Z=3) Since the number of electrons in the outermost shell is 1, hence the valency of the atom will be 1.


Q15Multiple choice

The electron distribution in an aluminium atom is:

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Correct option: A
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Worked solution

Ans: (a) 2, 8, 3

Explanation: The atomic number of aluminium is 13 and the first shell can have at the most two electrons. Hence, option (a) is correct.


Q16Multiple choice

Which of the following in Fig. 4.2 do not represent Bohr’s model of an atom correctly?


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Correct option: C
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Worked solution

Ans: (c) (ii) and (iv)

Explanation: The first shell cannot have more than 2 electrons and the second shell cannot have more than 8 electrons.


Q17Multiple choice

Which of the following statements is always correct?

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Correct option: A
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Ans: (a) An atom has an equal number of electrons and protons.

Explanation: An atom is electrically neutral. As a result, the number of protons and electrons should be equal.


Q18Multiple choice

Atomic models have been improved over the years. Arrange the following atomic models in the order of their chronological order:

(i) Rutherford’s atomic model

(ii) Thomson’s atomic model

(iii) Bohr’s atomic model


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Correct option: C
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Worked solution

Ans: (c) (ii), (i) and (iii)