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CBSE Questions for Class 9 Chemistry Structure Of The Atom Quiz 3 - MCQExams.com
CBSE
Class 9 Chemistry
Structure Of The Atom
Quiz 3
In magnesium, the number of electrons in $$K$$ shell is:
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$$2$$
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$$8$$
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$$3$$
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$$1$$
Explanation
Atomic number of $$Mg$$ is $$12$$.
So, the number of electrons in the different shells is:
$$K = 2, L = 8, M = 2$$.
Which of the following elements has three shells with no shells having even number of outer electrons?
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Mg
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Si
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S
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None of the above
Explanation
The electronic configuration of Mg is $$2,\,8,\,2$$. The electronic configuration of Si is $$2,\,8,\,4$$. The electronic configuration of S is $$2,\,8,\,6$$. Therefore, every option has even electrons in its outermost shell.
Bohr modified the ___________ by adding that the electrons move in orbits of fixed size and energy.
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Rutherford's model
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Dalton's model
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Thomson's model
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Goldstein's model
Explanation
Bohr modified the Rutherford model by adding that the electrons move in orbits of fixed size and energy. Electrons revolve around the nucleus in concentric circular orbits at fixed distance from the nucleus.
These are stationary orbits and the energy of electrons in these orbits is constant.
Thomson showed that the stream of particles in cathode ray tube is made up of small particles which are a component of the atom and is:
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neutral
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negatively charged
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positively charged
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both A and B
Explanation
Thomson discovered electrons using the cathode ray tube. It has been previously seen that if a electric current is passed through a vacuum tube, a glowing stream is formed. Thomson found that the mysterious glowing stream would bend toward a positively charged electric plate. He concluded that the stream is negatively charged. He also concluded based on his experiments that the negative stream has negatively charged particles that he called corpuscles (later renamed electrons).
Plum Pudding Model of the Atom was given by:
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Thomson
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Rutherford
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Bohr
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Chadwick
Explanation
J. J. Thomson's model was also known as the plum pudding model according to which positive charge is distributed uniformly throughout the atom and negative charge is dispersed in it.
Hence, the correct option is $$A$$
What is a neutron?
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A positively charge particle
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A negatively charged particle
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A neutral particle
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None of these
Explanation
Neutron is a neutral particle which exist in the nucleus. It decides the mass of the atom.
Thomson's model of atom is also known as:
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water-melon model
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raisin pudding model
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plum pudding model
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Rutherford's model
Explanation
Thomson's model of atom is also known as
water-melon model,
raisin pudding model and
plum pudding model. The representation of the atom in Thomson's model represents a pudding and a watermelon.
Which of the following statement is false?
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Proton has a positive charge.
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Neutron has no charge.
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Electrons are found in regions of the atom called orbitals.
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Electrons has a greater mass than the protons.
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Protons and neutrons form the nucleons of the atom.
Explanation
The electron has less mass.
A proton and a neutron have effectively the same mass. A proton (or a neutron) has approximately $$1837$$ times more massive than an electron.
The element used by Rutherford in his famous scattering experiment was
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Gold
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Tin
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Silver
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Lead
Explanation
Rutherford's alpha-particle scattering experiment is also known as the gold foil experiment as Rutherford used gold foil in it.
Option $$A$$ is correct.
A neutral atom of fluorine has a mass number of $$19$$ and an atomic number of $$9$$. How many neutrons does it have?
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$$10$$
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$$9$$
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$$19$$
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$$28$$
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It is impossible to determine from the information given.
Explanation
Mass number, $$A=19$$
Atomic number, $$Z=9$$
Number of neutrons=$$A-Z=19-9=10$$
The mass number of an element isIf it has 8 neutrons then valence shell of this element is.
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K
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L
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M
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N
Explanation
Since mass number $$(A) = 16$$ and number of neutrons $$= 8$$
Atomic number$$(Z) = 16-8 = 8$$
Therefore, electronic configuration will be 2,6
Hence, $$L$$ is the valence shell and there are 6 electrons in it.
Goldstein's work with canal rays was apparently the first observation of the:
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protons
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electrons
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neutrons
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atoms
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, known as a proton. Proton has a charge, equal in magnitude but opposite in sign to that of the electron.
So, the correct option is $$A$$
What is the atomic number of oxygen?
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$$9$$
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$$15$$
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$$8$$
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$$16$$
Explanation
The atomic number of oxygen is $$8$$.
The mass of an atom is given by the sum of the number of protons and neutrons present in the nucleus. Also, the atomic number is the number of protons present in the nucleus. Since the number of neutrons present in oxygen is $$8$$, hence the atomic number of $$O$$ is $$8$$.
The first model of an atom is given by:
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Neils Bohr
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Ernest Rutherford
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J.J. Thomson
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Eugen Goldstein
Explanation
$$J.J.\ Thomson$$ gave the first model of an atom.
In Rutherford experiment, most of the alpha particles go straight through the foil because________
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Alpha particles are much heavier than electron.
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Alpha particles are positively charged.
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Alpha particles move with high velocity.
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Most part of the atom is empty.
The number of orbitals in $$n=3$$ are :
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$$1$$
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$$4$$
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$$9$$
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$$16$$
Explanation
Given :
No. of shells $$\left( n \right) = 3 $$
Formula to calculate the number of orbitals is, n
umber of orbitals $$= {n}^{2}$$
$$\therefore \text {Number of orbitals} = $$ $$ {n}^{2} = {\left( 3 \right)}^{2} = 9$$
Therefore, the option is $$C$$.
What will be the number of protons, neutrons, and electrons present in
$$^{59}_{27}Co$$ respectively,
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$$27, 32, 27$$
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$$27, 32, 26$$
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$$59, 27, 29$$
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$$59, 27, 27$$
Explanation
In a neutral atom, number of protons = number of electrons
Here, the number of protons and electrons is $$27$$ and the number of neutrons $$= 59-27 = 32$$
Hence, option $$A$$ is correct.
Calculate the number of neutrons present in the nucleus of an element $$X$$ which is represented as
$$_{15}X^{31}$$.
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20
0%
25
0%
12
0%
16
Explanation
The mass number is the sum of the number of protons and the number of neutrons.
Mass number = Number of Protons + Number of Neutrons
Therefore, number of Neutrons = Mass number - Number of Protons $$= 31-15 = 16$$
Which of the following is the correct atomic number of Fluorine?
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6
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7
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8
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9
Explanation
The atomic number of fluorine is $$9.$$. Therefore, the correct option is D.
The number of protons present in the nucleus of an atom is known as the atomic number.
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True
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False
Explanation
The number of protons present in the nucleus of an atom is known as the atomic number.
Therefore, the given statement is true.
Atomic number and mass number are not much different from each other. They are same.
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True
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False
Explanation
$$\text{False}$$
1. Atomic number: The number of protons present in the nucleus of an atom is known as the atomic number. It is denoted by Z.
2. Atomic mass number: The total number of protons and neutrons present in the nucleus of an atom is known as the mass number. It is denoted by A. Generally atomic number and mass number of the atom of an element is represented by a symbol $$^{A}_{Z}X$$
As the atomic number and mass number are not the same hence given statement is false.
What is the mass number of potassium $$_{19}K^{40}$$,?
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60
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45
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90
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40
Explanation
The mass number of potassium $$(A)= 40$$. Therefore, the option $$D$$ is correct.
The total number of protons and neutrons present in the nucleus of an atom is known as mass number.
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True
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False
Explanation
The total number of protons and neutrons present in the nucleus of an atom is known as mass number. Therefore, the given statement is true.
Which term can be used for the number of protons present in an atom?
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Atomic mass
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Atomic number
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Mass number
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None of the above
Explanation
The number of protons present in the nucleus of an atom is known as atomic number. It is also equal to number of electrons in the atom. So, option B is correct.
Atomic mass is the mass of an atom. Mass number is the total number of protons and neutrons in an atom.
The mass number of a neutral atom is 31 electrons. What is the atomic number of this atom?
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75
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25
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15
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45
Explanation
The M shell of the atom contains 5 electrons, is given. K and L shell will contain 2 and 8 electrons, respectively. So, the atomic number of this atom will be equal to total number of electrons as it is a neutral atom.
Atomic number = (2 + 8 + 5) = 15.
Calculate the atomic number and mass number in the following case-
The atom of an element is made up of $$4$$ protons, $$5$$ neutrons and $$4$$ electrons.
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5, 8
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4, 9
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2, 9
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5, 10
Explanation
Protons $$= 4,$$ neutrons $$= 5,$$ electrons $$= 4$$, Atomic number $$= 4,$$
Mass number $$= 4 + 5 = 9$$
What is the term used for the number of protons and neutrons present in the nucleus of an atom?
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Atomic number
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Mass number
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Atomic mass
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Molecular mass
Explanation
The number of protons and neutrons present in the nucleus of an atom is known as mass number. The mass number is represented by $$A$$.
What is the mass number of $$_{17}Cl^{35}$$ ?
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21
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25
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39
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35
Explanation
The mass number of chlorine is 35. Therefore, the correct option is $$D.$$
The total number of neutrons in all isotopes of hydrogen is equal to:
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6
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2
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4
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3
Explanation
Hydrogen has 3 isotopes.
$$_{1}^{1}\textrm{H} $$
$$_{1}^{2}\textrm{H}$$
$$_{1}^{3}\textrm{H}$$
neutron 0
1
2
proton 1
1
1
The total number of neutrons in all the isotopes of Hydrogen $$=0+1+2=3$$.
In Rutherford's 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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alpha particles move with high velocity
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most part of the atom is empty
Explanation
The observation that most alpha particles passed straight through the gold foil led Rutherford to conclude that the positive charge in an atom is concentrated in a very small area that is called nucleus.
Atoms have mostly empty space. Electrons, which are negatively charged, are distributed throughout this space but take up a very small part of it.
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