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CBSE Questions for Class 9 Chemistry Structure Of The Atom Quiz 13 - MCQExams.com
CBSE
Class 9 Chemistry
Structure Of The Atom
Quiz 13
Valency expresses:
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total electrons in an atom
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atomicity of an element
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oxidation number of an element
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combining capacity of an element
Explanation
Valency is the number of electrons lost, gained, or shared by an atom during a chemical reaction. Elements in the same group have the same valency because they have the same number of electrons in the outermost shell.
Therefore, valency is combining the capacity of an element.
Hence, the correct option is $$D$$.
If the Thomson model is correct what should be the observation in the $$\alpha - ray$$ scattering experiment
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All the $$\alpha - ray$$ should pass through the gold foil
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Only few $$\alpha - ray$$ should pass through the gold foil
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98% of $$\alpha - ray$$ should get reflected back
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Both B & C
Explanation
According to Thomson model, positive charge is uniformly distributed with electrons embedded in it like seeds of watermelon.
$$\alpha$$ ray is much heavier than proton as $$ \alpha=^{4}_{2}He^{2+}$$.
Alpha particle has mass four times that of a proton. So since the positive charge is not concentrated in one place. So alpha ray will pass through the gold foil as there is no concentrated positive charge to stop it.
Hence, option $$A$$ would be the answer, if the Thomson model is correct.
The proton and neutron are collectively called as:
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Deutron
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Positron
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Meson
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Nucleon
Explanation
The nucleus consists of protons and neutrons, collectively both are called nucleons.
Proton was discovered by:
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Chadwick
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Thomson
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Goldstein
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Bohr
Explanation
In 1886, Eugen Goldstein discovered canal rays or positive rays which led to the discovery of proton in 1920 by Ernest Rutherford.
From the given options, only Goldstein is related to the discovery of the proton.
Hence the correct option is $$C$$.
The first three radius ratio of Bohr orbits
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$$1:0.5:0.5$$
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$$1:2:3$$
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$$1:4:9$$
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$$1:8:27$$
Rutherford's experiment on scattering of particles showed for the first time that the atom has:
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electrons
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protons
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nucleus
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neutrons
Explanation
Rutherford's alpha-particle scattering experiment showed for the first time that an atom has a nucleus. He observed that some particles were being deflected, which indicated that the positive charges are confined to a small space in the atom. This positively charged portion of the atom is nucleus.
If an electron moves away from nucleus, its potential energy:
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decreases
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not changes
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increases
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none of these
Explanation
As an electron moves away from the nucleus, its potential energy increases.
Hence, option C is correct.
Total number of atom in one molecule of sulfur is____.
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2
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6
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4
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8
Explanation
Sulfur molecules have $$8$$ atoms in them because of their high catenation property.
$$S_8$$: Crown sulfur
Hence, option D is correct.
The nucleus of helium contains
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Four protons
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Four neutrons
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Two neutrons and two protons
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Four protons and two electrons
Explanation
Atomic mass of Helium is $$2$$ and atomic mass is $$4$$.
So, there are $$2$$ protons and $$2$$ neutrons in the nucleus of Helium.
Option $$C$$ is correct.
Atoms have void spaces. It was first suggest by
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Rutherford
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Thomson
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Lenard
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Dalton
Which of the following is not a correct statement according to Rutherford's atomic model?
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$$99\%$$ of mass of an atom is centered in the nucleus.
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Most of the part inside the atom is empty.
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The size of nucleus is very small in comparison to the atom.
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Electrons revolve around the nucleus in a fixed circular path.
Explanation
Based on his experiment,
Rutherford put forward the nuclear model of
an atom, which had the following features:
(i) There is a positively charged centre in
an atom called the nucleus. Nearly all
the mass of an atom resides in the
nucleus.
(ii) The electrons revolve around the
nucleus in circular paths.
(iii) The size of the nucleus is very small
as compared to the size of the atom.
The nucleus of an element contain 9 protons. Its valency would be.
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1
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3
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2
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5
Explanation
As nucleus of the element contains nine protons, its atomic number is 9. Hence, the electronic configuration of the element is $$2,7$$. It needs one more electron to attain the stable inert gas configuration. Hence, its valency is 1.
Therefore, option $$A$$ is correct.
The density of neutrals is of the order:
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$$10^3 \, kg/cc$$
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$$10^6 \, kg/cc$$
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$$10^9 \, kg/cc$$
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$$10^{11} \, kg/cc$$
The expression for Bohr's radius of an atom is
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$$r = \dfrac{n^2h^2}{4\pi^2me^4z^2}$$
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$$r = \dfrac{n^2h^2}{4\pi^2me^2z}$$
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$$r = \dfrac{n^2h^2}{4\pi^2me^2z^2}$$
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$$r = \dfrac{n^2h^2}{4\pi^2m^2e^2z^2}$$
Explanation
$$ r = \dfrac{n^{2}h^{2}}{4\pi^{2} e^{2}mZ} $$
Hence, option B is correct.
The ratio of the radii of the first three Bohr orbits is:
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$$1:5:33$$
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$$1:2:3$$
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$$1:4:9$$
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$$1:8:27$$
Explanation
$$r_n \propto n^2$$
Option C is correct.
The radius of the first Bohr orbit of hydrogen atom is $$r$$. The radius of the $$3^{rd}$$orbit would be:
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$$3r$$
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$$9r$$
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$$27r$$
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$$none\ of\ these$$
Explanation
$$r_n =r_0 \dfrac {n^2}{Z}\Rightarrow r_3 =r(3)^2 =9r \left(A / q, \dfrac {r_0}{Z}=r \right)$$
Option B is correct.
Which of the following is always a whole number?
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Atomic weight
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Atomic radius
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Atomic volume
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Atomic number
Explanation
Atomic weight is the mass of a single atom of an element. It may be fractional. Atomic radius (distance from an atom's nucleus to the outermost orbital of electrons) and atomic volume (average volume of one atom of an element) can be fractional as well.
Atomic number is the number of protons or electrons in an atom. Since this is countable, it's always a whole number. So, atomic number is the correct answer.
Neutron is a fundamental particle carrying:
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A charge of $$+1$$ unit and a mass of unit
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No charge and a mass of $$1$$ unit
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No charge and no mass
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A charge of $$-1$$ and a mass of $$1$$ unit
Explanation
Proton and $$e^{\ominus} $$ which are electrically charged, neutrons have no charge they are electrically neutral. The mass of a neutron is slightly greater than the mass of a proton,
which is 1 atomic
mass
unit (amu). (An atomic
mass
unit equals about $$1.67 \times 10^{−27} Kgs$$.)
Option (B) is correct.
Who proved that atoms had a nucleus?
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Ernest Rutherford
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James Chadwick
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J.J. Thomson
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None of these
The introduction of a neutron into the nuclear composition of an atom would lead to a change in:
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The number of the electrons also
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The chemical nature of the atom
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Its atomic number
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Its atomic weight
Explanation
The number of protons represents the atomic number of an element.
The total number of protons and neutrons in an atom represents the mass number (atomic weight) of that element. So, the introduction of a neutron to an atom leads to an increase in mass number by one unit.
Hence, option $$D$$ is correct.
Nucleons are:
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Protons and electrons
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Protons and neutrons
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Electrons and neutrons
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Electrons, protons and neutrons
Explanation
Nucleon, either of the subatomic particles, proton
(positively charged)
and neutron(neutral), constituting atomic nuclei.
Hence, option $$B$$ is correct.
Which of the following has zero valency?
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Sodium
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Beryllium
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Aluminium
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Krypton
Explanation
Noble Gases have zero valencies. Among the given options, only krypton is a noble gas.
Hence, Option "D" is the correct answer.
$$_{18} Ar^{40} , \ _{20} Ca^{40}$$ and $$_{19} K^{40}$$ are:
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Isomers
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Isotopes
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Isobars
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Isotones
Explanation
Atoms of different elements having different atomic numbers but the same mass number are called isobars. In the given question, $$Ar$$, $$Ca$$, and $$K$$ all have the same mass number. Hence the correct option is C.
Rutherford’s $$\alpha-$$ particle scattering experiment led to the discovery of;
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Nucleus
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Electrons
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Atoms
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Neutrons
Explanation
Rutherfords alpha particle scattering experiment led to the discovery of nucleus.
Goldsteins experiments which involved passing high voltage electricity through gases at very low pressure resulted in the discovery of:
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Electron
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Proton
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Nucleus
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Neutron
Explanation
E. Goldstein in 1886 discovered the presence of new radiations in a gas discharge and called them canal rays. These rays were positively charged radiations which ultimately led to the discovery of another sub-atomic particle, called proton.
Correct option is $$B$$.
The presence of electrons outside the nucleus and nucleus at the centre of the atom was suggested by:
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Electrons by J.J. Thomson and nucleus by E. Goldstein
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Electrons by J. Chadwick and nucleus by E. Rutherford
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Electrons by J.J. Thomson and nucleus by E. Rutherford
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Electrons by E. Rutherford and nucleus by J.J. Thomson
Explanation
The presence of electrons outside the nucleus was suggested by J.J. Thomson and the presence of nucleus at the centre of the atom was suggested by E. Rutherford.
Hence the correct option is $$C$$.
Which of the following statements about Rutherford’s model of atom are correct?
(i) Proposed that nearly all
the mass of an atom resides in the
nucleus.
(ii) Established that the $$\alpha$$–particles are four times as heavy as a hydrogen atom.
(iii) Considered
the nucleus as positively charged.
(iv) Agreed with Thomson’s model.
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(i) and (iii)
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(ii) and (iii)
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(i) and (iv)
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only (i)
Explanation
Based on his experiment,
Rutherford put forward the nuclear model of
an atom, which had the following features:
(i) There is a positively charged centre in
an atom called the nucleus. Nearly all
the mass of an atom resides in the
nucleus.
(ii) The electrons revolve around the
nucleus in circular paths.
(iii) The size of the nucleus is very small
as compared to the size of the atom.
Which of the following in figure do not represent Bohr’s model of an atom correctly
?
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(i) and (ii)
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(ii) and (iii)
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(ii) and (iv)
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(i) and (iv)
Explanation
According to Bohr's Model, the first shell cannot have more than 2 electrons and the second shell cannot have more than 8 electrons.
Hence correct option is (C).
Tick the appropriate answer.
Which one of the following scientists put forward the theory regarding the extra-nuclear structure of the atom ?
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James Chadwick
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John Dalton
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Rutherford
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Niels Bohr
Explanation
Niels Bohr of the following scientists put forward the theory regarding the extra-nuclear structure of the atom.
The sum of number of protons and number of neutrons present in the nucleus of an atom is called its
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mass number
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atomic number
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number of electrons
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all of the above
Explanation
The mass number refers to the sum of the number of protons and neutrons present in the nucleus of an atom and denoted by A.
Mass number = Number of protons + Number of neutrons.
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