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Science M.C.Q-[Che-1M]

Structure of the Atom · CBSE STD 9 (CBSE - English Medium). 27 questions.

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M.C.Q-[Che-1M]

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27 questions · timed · auto-graded

Question 11 Mark
Which of the following statement is correct about the atom of and element?
  1. An atom can have only protons and neutrons but no electrons.
  2. An atom can have only electrons ad neutrons but no protons.
  3. An atom can have only electron and proton but o neutron.
  4. an atom must always have a proton, neutron and electron.
Answer
  1. An atom can have only electron and proton but o neutron.

Explanation:

An atom must have a proton and an electron, but it may not have a neutron.

For example: In hydrogen atom, there is 1 proton, 1 electron but no neutron.

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Question 21 Mark
Which of the following represents the correct electron distribution in magnesium ion?
  1. 2, 8
  2. 2, 8, 1
  3. 2, 8, 8
  4. 2, 8, 7
Answer
  1. 2, 8

Explanation:

Magnesium ion, Mg2+ has 10 electrons; so, its electronic configuration is 2, 8.

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Question 31 Mark
Which of the following is the correct electronic configuration of sodium?
  1. 2, 8, 1
  2. 8, 2, 1
  3. 2, 1, 8
  4. 2, 8, 2
Answer
  1. 2, 8, 1

Explanation:

2, 8, 1 is the correct electronic configuration as the first shell can accommodate 2 electrons and second shell can accommodate 8 electrons. When the inner shell is full, electrons are filled in the outer shell.

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Question 41 Mark
Which of the following elements does not exhibit electrovalency?
  1. Calcium.
  2. Chromium.
  3. Carbon.
  4. Cadmium.
Answer
  1. Carbon.

Explanation:

Carbon has 4 electrons in its outermost orbit. It completes its octet by sharing 4 electrons.

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Question 51 Mark
Which f the following statement is always correct?
  1. An atom has equal number of electrons and protons.
  2. An atom has equal number of electrons and neutrons.
  3. An atom has equal number of protons and neutrons.
  4. An atom has equal number of electrons, protons and neutrons.
Answer
  1. An atom has equal number of protons and electrons.

Explanation:

An atom always has equal number of protons and electrons in order to maintain electrical neutrality.

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Question 61 Mark
The subatomic particle called electron was discovered by:
  1. J.J. Thomson
  2. Neils Bohr
  3. James Chadwick
  4. D. E. Goldstein
Answer
  1. J.J. Thomson

Explanation:

J.J. Thompson discovered electrons by conducting a cathode-ray experiment.

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Question 71 Mark
There are two species represented as 35Cl and 37Cl. Which of the following statement is correct regarding these species?
  1. They have different chemical properties.
  2. Their physical properties are the same.
  3. They have the same number of protons.
  4. They are isobars of the same element.
Answer
  1. They have the same number of protons.

Explanation:

As the mass numbers are different, the correct option is (c). They have the same number of protons.

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Question 81 Mark
There are four elements P, Q, R and S having atomic numbers of 4, 18, 10 and 16 respectively. The element which can exhibit covalency as well as electrovalency will be:
  1. P.
  2. Q.
  3. R.
  4. S.
Answer
  1. S.

Explanation:

Element S has electronic configuration 2, 8, 6. It can exhibit covalency as well as electrovalency.

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Question 91 Mark
The radioactive isotope used in the treatment of cancer is:
  1. Plutonium–239
  2. Arsenic–74
  3. Cobalt–60
  4. Iodine–131
Answer
  1. Cobalt–60

Explanation:

Cobalt-60 is used in the treatment of cancer. High-energy gamma rays emitted by cobalt-60 isotopes destroy cancerous tumours.

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Question 101 Mark
The particle not present in an ordinary hydrogen atom is:
  1. Proton.
  2. Neutron.
  3. Nucleus.
  4. Electron.
Answer
  1. Neutron.

Explanation:

A hydrogen atom 11HH11 has 1 proton and 1 electron, but it does not have any neutron.

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Question 111 Mark
The number of valence electrons in a sulphide ion, S2-, is:
  1. 16
  2. 10
  3. 9
  4. 8
Answer
  1. 8

Explanation:

Atomic number of a sulphur atom S is 16. It has 6 electrons in its outermost orbit. After gaining 2 electrons it becomes S2-. So, now the outermost orbit will have 8 electrons.

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Question 121 Mark
The number of valence electrons in a graphite atom is:
  1. 2
  2. 4
  3. 3
  4. 5
Answer
  1. 4

Explanation:

Graphite is an allotrope of carbon. It is made up of all C atoms. The atomic number of carbon is 6; so, the number of valence electrons is 4.

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Question 131 Mark
The number of electrons in the atom of an element X is 15 and the number of neutrons is 16. Which of the following is the correct representation of an atom of this element?

  1. $^{31}_{15}\text{X}$

  2. $^{31}_{16}\text{X}$

  3. $^{16}_{15}\text{X}$

  4. $^{15}_{16}\text{X}$

Answer
  1. $^{31}_{15}\text{X}$

Explanation:

In an atom, the number of electrons is equal to number of protons, which in turn is equal to the atomic number of the element. Also, the sum of number of protons and neutrons represents the mass number of the element.

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Question 141 Mark
The mass number of two atoms X and Y is the same (40 each) but their atomic numbers are different (being 20 and 18 respectively). X and Y are examples of:
  1. Chemically similar atoms.
  2. Isotopes.
  3. Solid and liquid metals.
  4. Isobars.
Answer
  1. Isobars.

Explanation:

Isobars are the atoms of different elements with same mass number but different atomic numbers.

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Question 151 Mark
The isotopes of an element contain:
  1. Same number of neutrons but different number of protons.
  2. Same number of neutrons but different number of electrons.
  3. Different number of protons as well as different number of neutrons.
  4. Different number of neutrons but same number of protons.
Answer
  1. Different number of neutrons but same number of protons.

Explanation:

Isotopes are the atoms of the same element with the same atomic number but different mass numbers. It means that they have the same number of protons and electrons but different number of neutrons.

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Question 161 Mark
The ion of an element has 3 positive charges. The mass number of atom of this element 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
  1. 10

Explanation:

Mass number of the element = 27

Number of neutrons = 14

Number of protons = mass number - number of neutrons

= 27 - 14 = 13

As the ion of this element has 3 positive charges, it means that it has lost 3 electrons. Therefore, there are now 10 electrons in the ion.

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Question 171 Mark
The four atomic species can be represented as follows. Out of these, the two species which can be termed isobars are:

  1. $^{201}_{\ 60}\text{X}$

  2. $^{201}_{\ 61}\text{X}$

  3. $^{200}_{\ 58}\text{X}$

  4. $^{203}_{\ 60}\text{X}$

  1. (i) and (ii)
  2. (ii) and (iii)
  3. (i) and (iii)
  4. (i) and (iv)
Answer
  1. (ii) and (iii)

Explanation:

$^{201}_{\ 61}\text{X and }^{200}_{\ 58}\text{X}$ are isobars because they have the same mass number but different atomic numbers.

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Question 181 Mark
The first model of an atom was given by:
  1. Neils Bohr
  2. Ernest Rutherford
  3. J.J. Thomson
  4. Eugen Goldstein
Answer
  1. J.J. Thomson

Explanation:

J.J. Thompson gave the first model of an atom.

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Question 191 Mark
The correct electronic configuration of a chloride ion is:
  1. 2, 8
  2. 2, 8, 4
  3. 2, 8, 8
  4. 2, 8, 7
Answer
  1. 2, 8, 8

Explanation:

Chloride ion, Cl- has 18 electrons so, its electronic configuration is 2, 8, 8.

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Question 201 Mark
The atomic numbers of four elements A, B, C and D are 12, 13, 15 and 3 respectively. The element which cannot form a cation is:
  1. A
  2. B
  3. C
  4. D
Answer
  1. C

Explanation:

Element C has 15 electrons; so, the electronic configuration is 2, 8, 5. This element will gain 3 electrons in order to complete its octet; so, it cannot form cations.

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Question 211 Mark
The atomic number of an element X is 8 and that of element Y is 4. Both these elements can exhibit a valency of:
  1. 1
  2. 2
  3. 3
  4. 4
Answer
  1. 2

Explanation:

Atomic number of element X is 8.

Electronic configuration is 2, 6. It will gain 2 electrons to complete its octet; so, its valency is 2.

Atomic number of Y is 4.

Electronic configuration is 2, 2. It will lose 2 electrons in order to completely fill its outermost orbit. So, the valency of Y is also 2.

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Question 221 Mark
Rutherford’s alpha particle scattering experiment led to the discovery of:
  1. Nucleus.
  2. Electrons.
  3. Protons.
  4. Neutrons.
Answer
  1. Nucleus.

Explanation:

Rutherford conducted an experiment using alpha particles which led to the discovery of a nucleus situated at the centre of an atom.

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Question 231 Mark
In a sample of ethyl ethanoate (CH3COOC2H2), 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 protons.
  3. The two oxygen atoms are isotopes.
  4. The two oxygen atoms are isobars.
Answer
  1. The two oxygen atoms are isotopes.

Explanation:

As the number of protons is same but the number of neutrons is different, the mass number of the two oxygen atoms is different. So, these two are isotopes of each other.

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Question 241 Mark
Goldstein’s experiments which involved passing high voltage electricity through gases at very low pressure resulted in the discovery of:
  1. Electron.
  2. Proton.
  3. Nucleus.
  4. Neutron.
Answer
  1. Proton.

Explanation:

Goldstein’s experiment, which involved passing high-voltage electricity through gases at very low pressure, resulted in the discovery of protons.

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Question 251 Mark
Four elements W, X, Y and Z contain 8, 11, 9 and 17 protons per atom respectively. The element which cannot form an anion is most likely to be:
  1. W
  2. X
  3. Y
  4. Z
Answer
  1. X

Explanation:

Element X can’t form anions as the outermost orbit contains only 1 electron. The atom will rather lose this electron to complete its octet and will become a cation.

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Question 261 Mark
For an element, Z = 9. The valency of this element will be:
  1. 4
  2. 2
  3. 1
  4. 3
Answer
  1. 1

Explanation:

Atomic number is 9, which means that number of electrons is also 9. Electronic configuration is 2 , 7. So, the atom will gain 1 electron to complete its octet. Therefore, the valency is 1.

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Question 271 Mark
Elements having valency ‘one’ are:
  1. Always metals.
  2. Always non-metals.
  3. Always metalloids.
  4. Either metals or non-metals.
Answer
  1. Either metals or non-metals.

Explanation:

Elements with valency 1 can be either metals or non-metals. When an atom loses one electron to gain stability, it is a metal. When an atom gains an electron to complete its octet it is a non-metal.

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