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CBSE Questions for Class 9 Chemistry Structure Of The Atom Quiz 7 - MCQExams.com
CBSE
Class 9 Chemistry
Structure Of The Atom
Quiz 7
An atom is electrically .....
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Neutral
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Negative
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Positive
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None of these
Neutron is a positively charged sub-atomic particle.
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True
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False
Explanation
A neutron is a sub-atomic particle with no net electrostatic charge, with a similar mass to a proton. It is charge neutral by nature. Therefore the given statement is false.
Which of the following has the greatest mass?
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Electron
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Proton
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Neutron
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Hydrogen cation
Explanation
Neutron has the greatest mass. Proton is a subatomic particle with the symbol $$p$$ and positive electric charge of $$+1$$ elementary charge and a mass slightly less than that of the neutron.
Mass of neutron is $$1.6749\times10^{-27} \ kg$$
Mass of electron is $$9.109 \times 10^{-31} \ kg$$
Mass of proton is $$1.67262 \times 10^{-27} \ kg$$
Mass of hydrogen cation is $$1.6735 \times 10^{-27} \ kg$$
Hence, the correct option is C.
Deflection back of a few particles by large angle on hitting thin foil of gold in Rutherford's experiment showed that
:
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nucleus is dense
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nucleus is small
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both A and B
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electrons create hinderance in the movement of $$\displaystyle \alpha $$-particles
Explanation
It was observed in Rutherford's experiment of gold foil that very few $$\alpha$$ particles were deflected back by large angles. The deflection of only a very few
$$\alpha$$ particles
helped him to conclude that the
nucleus occupies very little space in an atom
. He also concluded
that the nucleus would be dense to deflect the
$$\alpha$$ particles by large-angle.
Hence option C is correct.
The radius of an atom is of the order of:
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10$$^{-10}$$ cm
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10$$^{-13}$$ cm
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10$$^{-15}$$ cm
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10$$^{-8}$$ cm
Explanation
On the basis of scattering experiments, Rutherford proposed the model of an atom, which is known as the nuclear atomic model.
According to this model -
(i) An atom consists of a heavy positively charged nucleus where all the protons are present.
(ii) The volume of the nucleus is very small and is only a minute fraction of the total volume of the atom.
Nucleus has a radius of the order of $$10^{-13}$$ cm and the atom has a radius of the order of $$10^{-8}$$ cm.
In Rutherford's $$\alpha$$-particle scattering experiment, a very small fraction of $$\alpha$$ - particles were deflected by $$180^{\circ}$$. What did he conclude from this observation?
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All the positive charge and mass of the atom occupy very little space.
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Most of the space inside the atom is empty.
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All the positive charge and mass of the atom were concentrated in a very small volume.
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Both A and B
Explanation
We conclude from this observation that a
ll the positive charge and mass of the atom were concentrated in a very small volume. Therefore, a very small fraction of $$\alpha$$-particles are deflected by $$180^{\circ}$$.
Isotone of an element has :
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Same number of electron
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Same number of protons
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Same number of neutrons
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Same number of neutrons & protons
Explanation
Isotone of an element has same no. of neutrons
The space between a proton and electron in hydrogen atom is
:
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full of air
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full of ether
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full of electromagnetic radiations
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empty
Explanation
Hydrogen atom contains one proton in the nucleus and one electron outside the nucleus.
The space between a proton and electron in hydrogen atom is empty.
Alpha-particles that come closer to nuclei in Rutherford's alpha particle scattering experiment:
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are deflected more
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are deflected less
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make more collisions
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None of the above
Explanation
In the $$\alpha$$-particle experiment as the alpha particles come closer to the nucleus it deflects more, because $$\alpha$$-particle and the nucleus both are positively charged. And positive charge repel each other and this electrostatic force is inversely squared proportional to the distance between $$\alpha$$-particle and nucleus.
Option 'A' is correct.
Following conclusions were drawn from the given figure :
I. There is a positively charged centre in an atom called the nucleus.
II. An atom consists of a positively charged sphere and the electrons are embedded in it.
III. The electrons revolve around the nucleus in well-defined orbits.
IV. The size of the nucleus is very small as compared to the size of the atom
V. Only certain special orbits known as discrete of electrons are allowed inside the atom.
Choose the correct statements.
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I, II and III
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II, III and V
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I, III and IV
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All of these
Explanation
On the basis of scattering experiments, Rutherford proposed the model of an atom, which is known as the nuclear atomic model. According to this model -
(i) An atom consists of a heavy positively charged nucleus where all the protons are present.
(ii) The volume of the nucleus is very small and is only a minute fraction of the total volume of the atom.
There is empty space around the nucleus called the extranuclear part. In this part electrons are present. The no. of electrons in an atom is always equal to no. of protons present in the nucleus. As the nuclear part of the atom is responsible for the mass of the atom, the extranuclear part is responsible for its volume.
Electrons revolve around the nucleus in closed orbits with high speeds.
Which of the following is the characteristic feature of an isotopes?
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Same number of electrons and protons but different number of neutrons
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Same number of electrons but different number of protons
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Same number of neutrons but different number of electrons
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None of the above
Explanation
The characteristic feature of an isotope is that it has the same number of electrons and protons but a different number of neutrons.
The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number.
For example, carbon has three isotopes $$C^{12}$$, $$C^{13}$$, and $$C^{14}$$. All the three have 6 protons, but their neutron numbers are 6, 7, and, 8 respectively. Hence option A is correct.
Rutherford's alpha Scattering experiment showed that:
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the atoms were smashed up by alpha particles
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the atoms consisted of protons in a matrix of electrons
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the nucleus was quite large and positively charged
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the nucleus was very small and positively charged
Explanation
Rutherford demonstrated that an atom contains the new features of high central charge concentrated into very small volume in comparison to the rest of the atom and with this central volume also contains the bulk of the atomic mass of the atom.
When alpha particles were bombarded on a gold foil, most of the alpha particles passed through undeflected. This result indicates that most of the volume of a gold atom consists of:
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nucleus
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neutrons
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protons
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unoccupied space
Explanation
When alpha particles were bombarded on a gold foil, most of the alpha particles passed through undeflected. This result indicates that most of the volume of a gold atom consists of unoccupied space. This experiment is called the Rutherford experiment. So the answer is D.
Mass number of all elements represents number of ______________.
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protons and neutrons
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protons and electrons
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electrons and neutrons
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None of the above
Explanation
The mass number (A), or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.
The nuclides $$^{40}_{18}Ar$$ and $$^{41}_{19}K$$ are :
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isotopes
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isobars
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isotones
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none of these
Explanation
The two or more species of atoms or nuclei that have the same number of neutrons are called as isotones.
The nuclides $$^{40}_{18}Ar$$ and $$^{41}_{19}K$$ are isotones. Because they have the same number of neutron.
So, the correct option is $$C$$
If the radius of gold (Au) and platinum (Pt) atoms in pm is $$\displaystyle 100\sqrt{2}$$ and $$\displaystyle 90\sqrt{2}$$, respectively, find $$\displaystyle n_{Au}n_{Pt}$$.
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$$0.52$$
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$$0.68$$
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$$0.73$$
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$$0.74$$
Explanation
The number of atoms per unit volume is inversely proportional to the volume of one atom.
$$\displaystyle \frac {n_{Au}}{n_{Pt}} = \dfrac {V_{Pt}}{V_{Au}} =\dfrac {\dfrac {4}{3} \pi r^3_{Pt}}{\dfrac {4}{3} \pi r^3_{Au}}= (\dfrac {r_{Pt}}{r_{Au}})^3 = (\dfrac {90 \sqrt {2}}{100 \sqrt {2}})^3 = 0.73$$
Rutherford's model of atom could not hold good because:
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it did not account for the stability of an atom
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the atom did not have a nucleus and an electron
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it did not account for the attraction between a proton and an electron
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there is actually no space between the nucleus and the electron
Explanation
Rutherford demonstrated that an atom contains the new features of high central charge concentrated into a very small volume in comparison to the rest of the atom and this central volume also contains the bulk of the atomic mass of the atom.
Failure - An electron revolving around the nucleus at an accelerated pace loses energy following a spiral path and ultimately falls into the nucleus but the atoms are stable. So, he could not explain the stability of an atom.
In Rutherford's gold foil experiment:
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very few $$\alpha$$-particles are deflected back.
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most of $$\alpha$$-particles remain undeflected.
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some of $$\alpha$$-particles deflected by small angles.
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All of these
Nuclides having the same difference in mass number and atomic number, are known as
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isotones
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isomers
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isobars
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isotopes
Explanation
$$Number\ of\ neutrons = mass\ number - atomic\ number$$
Number of neutrons are equal to the difference in mass number and atomic number. And species having equal number of neutrons are known as isotone.
The experiment which led to the discovery of nucleus was performed by
:
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Goldstein
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J.J. Thomson
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Dalton
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Rutherford
Explanation
Rutherford concluded in his scattering experiment that all the positive charge is concentrated in small fraction of total volume of atom in the nucleus.
Option D
The atomic number of an element is $$11$$. Therefore the number of electrons in the M-shell of its atom is:
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$$2$$
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$$8$$
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$$1$$
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$$0$$
Explanation
$$M$$ shell of an atom means 3rd shell (K, L, M).
The electronic configuration of an atom having atomic number $$11$$ is $$2, 8, 1$$ which shows that the third shell contains $$1$$ electron.
Hence, option C is correct.
The number of electrons in the outermost orbit of the chlorine is
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$$1$$
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$$7$$
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$$2$$
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Not fixed
Explanation
The electronic configuration of chlorine is $$2, 8, 7$$. It shows the outermost orbit contains $$7$$ electrons.
The valence shell of calcium contains ___________.
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$$2$$ electrons
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$$4$$ electrons
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$$6$$ electrons
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$$8$$ electrons
Explanation
The valency shell means the outermost shell or orbit of an element which has valence electrons or outer electrons in it. The atomic number of calcium is
20
and its electronic configuration is
2
,
8
,
8
,
2
which shows that the outermost orbit or valency shell contains
2
electrons.
$$_7N^{15}$$ and $$_8O^{16}$$ are a pair of :
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isotopes
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isobars
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isotones
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none of them
Explanation
Two nuclides are isotones if they have the very same neutron number but different proton number.
Beta particles are essentially:
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neutrons
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protons
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electrons
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helium nuclei
Explanation
Beta particles are emitted when an element decays by radioactive $$\beta$$ decay. The particles are essentially $$[{ e }^{ - }]$$ electrons.
The nuclear model of the atom was suggested by:
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Bohr
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Rutherford
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Pauli
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Mendeleef
Explanation
Rutherford suggested highly charged centrally concentrated small volume called as atomic mass and this region is known as nucleus of atom and gave the nuclear model of atom.
The atomic number of potassium is $$19$$. Hence the number of electrons in the $$N$$- shell will be
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$$9$$
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$$1$$
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$$8$$
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$$2$$
Explanation
Atomic number of potassium is $$19$$. Electronic configuration is $$2, 8, 8, 1$$. Hence, the number of electrons in the $$N$$-shell is $$1$$.
The size of the nucleus is approximately :
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$$10^{-18}m$$
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$$10^{-10}m$$
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$$10^{-8}m$$
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$$None\ of\ these$$
Explanation
The size of nucleus is approximately of the order of $$10^{-15}m.$$
The chemical properties of an atom depend upon:
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valency
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atomic number
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number of isotopes
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atomic weight
Explanation
The chemical properties of an atom depend upon the atomic number. From the atomic number, we can get valence electrons that determines the chemical properties of it.
Rutherford's scattering experiment led to the conclusion that
:
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nucleus is very small in size
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nucleus is very heavy and carries positive charge
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most of the space in the atom is empty
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all of these
Explanation
Rutherford model of atom contained the features of a relatively high central charge concentrated into very small volume in comparison to the rest of the atom and this central region was named nucleus of the atom. Alpha particles are deflected at tiny concentrated center while for most of the part these rays go undeflected shows having large empty space.
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