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CBSE Questions for Class 9 Chemistry Structure Of The Atom Quiz 4 - MCQExams.com
CBSE
Class 9 Chemistry
Structure Of The Atom
Quiz 4
Which of the following is/are true as per Thomson's model of atom?
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An atom is not electrically neutral.
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An atom is a positively charged sphere with electrons embedded in it.
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Negative and positive charges in the atom are equal in magnitude.
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None of the above
Explanation
Thomson's model of atom states that:
1. An atom consists of a positively charged sphere with electrons embedded in it.
2. Total positive and negative charges in the atom are equal in magnitude. So, atom is electrically neutral.
In Rutherford experiment, most of the alpha particles go straight through the foil because:
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Alpha particles are much heavier than electrons
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Alpha particles are positively charged
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Most part of the atom is empty space
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Alpha particles move with high velocity
Explanation
Rutherford's model describes atom as a tiny, dense, positively charged core called the nucleus in which almost the entire mass is concentrated, around which electrons circle around at a certain distance. In his experiment, he bombarded a thin gold foil with alpha particles.
Rutherford reasoned that since most of the atom is empty, the alpha particles passed straight through the gold foil.
So, option C is correct.
In Rutherford's $$\alpha$$-rays scattering experiment, gold foils are used because of ___________.
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high malleability
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ductility
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high melting point
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high ionisation energy
Explanation
Malleability is the material's ability to form thin sheets. In Rutherford's ray scattering experiment, gold foil is used because of its high malleability. Very thin gold foil is used in the experiment and gold is capable of being rolled into extremely thin foils.
Which of the following point is not shown by the Rutherford alpha scattering
experiment?
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$$\alpha$$ - particle can come within a distance of the order of $$10^{-14} m$$ of the nucleus
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The radius of the nucleus is less than $$10^{-14} m$$
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Sattering follows coulombs law
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The positively charged parts of an atom move with extremely high velocities
Explanation
The conclusions of Rutherford's alpha scattering experiment do not include that the positively charged particles move with great velocities. The positively charged particles are present at the center of the atom called a nucleus.
The Bohr model of atoms:
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uses Einstein's photo electric equation
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predicts continuous emission spectra for atoms
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predicts the same emission spectra for all types of atoms
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assumes that the angular momentum of electrons is quantized
Explanation
Bohr model of an atom states that only those orbits are allowed where angular momentum of electron are integral multiple of $$nh/2\pi$$. These orbits have quantized energy and angular momentum associated with electron.
The model can be applied to hydrogen or hydrogen-like atoms to explain their line emission spectrum.
Option D is correct.
To which of the following is Bohr's theory applicable:
I) $$He^{+}$$
II) $$Li^{2+}$$
III) Tritium
IV) $$Be^{2+}$$
The correct combination is:
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III, IV
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I, II, III, IV
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I, II
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I, II, III
Explanation
Bohr's atomic model explains the spectra of single-electron atoms like $$H$$-atom. It does not explain the spectra of multi-electron atoms.
So the atoms which are isoelectronic and have the same electronic configuration are well explained by this atomic model.
$$He^+$$, $$Li^{2+}$$ and tritium $$_{ 1 }{ H }^{ 3 }$$ have same number of electrons as that of hydrogen atom i.e. $$1$$ while $$Be^{2+}$$ is formed by losing $$2e$$. So, it is a two-electron system.
Option D is correct.
Which of the following properties are similar for isotopes?
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Physical properties
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Chemical properties
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Both physical and chemical properties
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Neither physical nor chemical properties
Which of the following statement is true about Rutherford’s experiment?
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$$\beta $$-particles, which impinged on a metal foil and got absorbed
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$$\gamma $$-rays, which impinged on a metal foil and ejected electrons
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Helium atoms, which impinged on a metal foil and got scattered
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Helium nuclei, which impinged on a metal foil and got scattered
Explanation
According to Rutherford's experiment, $$\alpha-$$ particles or helium nuclei impinged on a metal foil and got scattered.
Hence, the correct option is D.
In Rutherford's alpha-ray scattering experiment, a screen is used to detect the alpha particles which is coated by:
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carbon black
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platinum black
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zinc sulphide
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poly tetrafluoro ethylene
Explanation
In Rutherford's alpha-ray scattering experiment, the alpha particles are detected using a screen
coated with zinc sulphide.
The electron distribution in an aluminium atom is:
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2, 8, 3
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2, 8, 2
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8, 2, 3
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2, 3, 8
Explanation
Atomic number of Al = 13.
K, L, M shell will accommodate 2, 8, 3 electrons ($$2n^2$$ rule).
Therefore, the electronic configuration is 2, 8, 3.
Which of the following 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
The electronic configuration of an atom of the element is derived using Bohr's formula $$2n^{2}$$, where $$n$$ is the no. of orbit.
According to this formula, the first shell can contain only 2 electrons and the second shell contain not more than 8 electrons.
Atomic models have been improved over the years. Arrange the following atomic models in the order of their chronological order.
(i) Rutherfords atomic model
(ii) Thomsons atomic model
(iii) Bohr's atomic model
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(i), (ii) and (iii)
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(ii), (iii) and (i)
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(ii), (i) and (iii)
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(iii), (ii) and (i)
Explanation
Sir J J Thomson in 1897 studied the characteristics of cathode rays and discovered protons.
Lord Rutherford in 1911 studied the atomic model and discovered the atomic nucleus.
Bohr later explained the stability of the atom which was not explained by the others in their atomic theory.
Rutherford's scattering experiment estimated the size of:
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atom
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electron
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neutron
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nucleus
Explanation
Rutherford's model compared the sizes of the atom and that of the nucleus. He estimated the size of the nucleus to be about 1/100,000 the size of the atom.
During the Rutherford's $$\alpha$$-particle scattering experiment, he concluded that:
(i) electrons have negative charge.
(ii) the mass and positive charge of the atom is concentrated in the nucleus.
(iii) neutron exists in the nucleus.
(iv) most of the space in atom is empty.
Choose the correct statements.
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(i) and (iii)
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(ii) and (iv)
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(i) and (iv)
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(iii) and (iv)
Explanation
In his gold foil experiment, Rutherford observed that most of the alpha particles which are positively charged particles went straight through the foil without any deflection so he concluded that most of the space in the atom is relatively empty.
Few alpha particles deflected by large angles with a $$180^0$$ made him conclude that mass and positive charge is concentrated at the centre of the atom.
Hence option (B) is correct.
In Thomson's model of the atom, which of the following statements is/are correct?
(i) The mass of the atom is assumed to be uniformly distributed over the atom.
(ii) The positive charge is assumed to be uniformly distributed over the atom.
(iii) The electrons are uniformly distributed in the positively charged sphere.
(iv) The electrons attract each other to stabilize the atom.
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(i), (ii) and (iii)
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(i) and (iii)
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(i) and (iv)
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(i), (iii) and (iv)
Explanation
According to T
homson, the model of an atom is similar to a Christmas pudding.
The electrons are studded like currants(decorated) in a positively charged sphere like Christmas pudding and the mass of the atom was supposed to be uniformly distributed.
Therefore (i), (ii) and (iii) are all correct.
Hence the correct option is A.
Rutherford's alpha ($$\alpha$$) particle scattering experiment resulted in discovery of:
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electron
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proton
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nucleus in the atom
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atomic mass
Explanation
Rutherford concluded from the $$\alpha$$-particle scattering experiment that:
(i) Most of the space inside the atom is empty because most of the $$\alpha$$-particles passed through the gold foil without getting deflected.
(ii) Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.
(iii) A very small fraction of $$\alpha$$-particles were deflected by very large angles, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.
On the basis of his experiment,
Rutherford put forward the nuclear model of an atom, which had the following features:
(i) There is a positively charged center 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 well-defined orbits.
(iii) The size of the nucleus is very small as compared to the size of the atom.
Rutherford's alpha particle scattering experiment shows the presence of nucleus in the atom.
It also gives the following important information about the nucleus of an atom :
(i) The nucleus of an atom is positively charged.
(ii) The nucleus of an atom is very dense and hard.
(iii) The nucleus of an atom is very small as compared to the size of the atom as a whole.
Rutherford model of the atom is also called Nuclear model of the atom.
Hence (C) is the correct option.
According to Rutherford's atomic theory, the path an electron takes while revolving around the nucleus will be
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circular
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spiral
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straight
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none of these
Explanation
According to Rutherford's atomic theory, the electrons revolve around the nucleus in circular paths. But, the revolution of the electron in a circular orbit is not expected to be stable. Any particle in a circular orbit would undergo acceleration. During acceleration, charged particles would radiate energy. Thus, the revolving electron would lose energy due to which the radius of revolutions will go on decreasing until it finally falls into the nucleus. The path the electron takes will be spiral and not circular.
Which of the following statements about Rutherford's model of an atom are correct?
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It considered the nucleus is positively charged.
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It established that the $$\alpha$$ -particles are four times as heavy as a hydrogen atom.
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It can be compared to the solar system.
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It was in agreement with Thomson's model.
Explanation
Therefore option A and C are correct.
Which of the statements are the drawbacks of Rutherford's model of an atom?
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The orbital revolution of the electron is not expected to be stable
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Any particle in a circular orbit would undergo a acceleration and the charged particles would radiate energy
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The revolving electron would lose energy and finally fall into the nucleus
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All of the above
Explanation
The drawback of Rutherford model is:
It can't explain the stability of an atom. As per the model, the orbital revolution of electrons around the nucleus is not stable as the revolving electrons in orbits will undergo acceleration and emit energy. This will result in loss of energy of electrons and they will ultimately fall into the nucleus.
Neon and chlorine have atomic numbers $$10$$ and $$17$$ respectively. Their valencies will be ______ and ______ respectively.
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$$1, 1$$
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$$1, 0$$
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$$0, 1$$
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$$0, 0$$
Explanation
The valency of $$Ne$$ is zero as it is a noble gas and thus does not take part in bond formation.
$$Cl$$ has electronic configuration: $$2, 8, 7$$.
Therefore, $$Cl$$ will accept one electron to attain stable noble gas configuration. Thus valency of $$Cl$$ is $$1$$.
Isotopes have same____but different____.
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atomic number, mass number
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mass number, atomic number
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number of neutrons, atomic number
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None of these
Explanation
Isotopes of an element have same atomic number and different mass numbers.
Gold is chosen by Rutherford for his $$\alpha$$-ray scattering experiment because:
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gold has high malleability
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gold has high ductility
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gold has high density
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gold is the least reactive element
Explanation
Malleability is a property of metals which can be beaten into sheets. For his experiment Rutherford needed a very thin sheet of metal and hence he selected gold metal which could be beaten into very thin sheet.
The conclusion of Rutherford from his $$\alpha$$-ray scattering experiment is:
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many particles were deflected from their path, indicating that the positive charge of the atom occupies very small space.
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many particles were deflected from their path, indicating that the positive charge of the atom occupies very large space.
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most of the space inside the atom is empty because most of the $$\alpha$$-particles passed through the gold foil without getting deflected.
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a very large fraction of alpha-particles were deflected by $$180^o$$, indicating that all the positive charges and mass of the gold atom were concentrated in a very small volume within the atom.
Explanation
The conclusion of Rutherford from his $$\alpha$$-ray experiment are:
(i) Most of the space inside the atom is empty because most of the alpha-particles passed through the gold foil without getting deflected.
(ii) Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.
(iii) A very small fraction of alpha-particles were deflected by $$180^\circ$$,
indicating that all the positive charges and mass of the gold atom were concentrated in a very small volume within the atom.
From the data he also calculated that the radius of the nucleus is about 105 times less than the radius of the atom.
The gap between electron and nucleus(proton) in hydrogen atom is:
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absolutely empty
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full of electromagnetic radiation
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full of air
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full of ether
Explanation
In an atom, protons are present in the nucleus and electrons are revolving in orbits around the nucleus. Therefore in a hydrogen atom, the space between one proton and one electron is empty.
The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements isWhat is the name given to such a pair of elements?
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Isotopes
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Isobars
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Both isotopes and isobars
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None of the above
Explanation
Isobars are atoms having the same mass number but a different atomic number. The pair has the same atomic mass which is 40 and different atomic number 20 and 18 respectively.
Bohr's model explains:
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the spectrum of hydrogen atom only
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the spectrum of any atom or ion having one electron only
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the spectrum of hydrogen molecule
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the solar spectrum
Explanation
Bohr's model successfully explained the spectrum of an atom or ion having one electron only.
Find out the valency of the atoms represented by the figure.
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(a) 0 (b) 0
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(a) 1 (b) 0
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(a) 0 (b) 1
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(a) 1 (b) 1
Explanation
Valency of an atom of an element is the number of electrons lost or gained by an atom in order to become stable.
Atom in diagram 'a' has completely filled outermost shell as it has 8 electrons in the outermost shell. hence it is stable. it need not lose or gain electrons in order to become stable.
Atom in diagram 'b' has 7 electrons in its valence shell. To have octet, it gains one electron and hence its valency is one.
Rutherford's $$\alpha-$$ particle scattering experiment led to the discovery of:
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electrons
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protons
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neutrons
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atomic nucleus
Explanation
During Rutherford's experiment, most of the $$\alpha$$ particles emitted from a radioactive source bounced back to the source when passed through a gold foil. This is possible only if positively charged heavy particle (nucleus) is present at the centre. Hence, this experiment led to the discovery of atomic nucleus.
$$_{18}Ar^{40}$$ and $$_{19}K^{40}$$ are a pair of:
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isomers
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isobars
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isotopes
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isotones
Explanation
$$Ar^{40}$$ and $$K^{40}$$ have same mass no. 40 but different atomic number, therefore, they are called isobars.
Size of the nucleus is:
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$$1A^0$$
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$$10^{-16}m$$
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$$10^{-15}m$$
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$$10^{-14}m$$
Explanation
According to Rutherford the nucleus size is $${ 10 }^{ -15 }m$$.
The size of the atom ranges from $$0.1$$ to $$0.5nm$$
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