# Topic: Nuclei (Test 1)

Topic: Nuclei
Q.1
What is the percentage of the mass of an atom concentrated in the nucleus?
A. 99.9
B. 79.9
C. 66.9
D. 50.9
Explaination / Solution:

A proton and a neutron have roughly 2000 times the mass of an electron. The numbers of an electron in a stable atom (not isotope) is equal to the electrons. So for most atoms, the nucleus will hold roughly 4000 times the mass of its electron cloud. Thus,
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Q.2
What is the unit of mass when measured on the atomic scale?
A. Kilogram
B. Gram
C. Milligram
D. Unified atomic mass unit
Explaination / Solution:

The unified atomic mass unit (u) is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest.

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Q.3
Atomic mass unit (u) is defined as ________ of the mass of the carbon () atom.
A. (110)th
B. (112)th
C. (114)th
D. (116)th
Explaination / Solution:

For standardization, a specific atomic nucleus (carbon-12) had to be chosen because the average mass of a nucleon depends on the count of the nucleons in the atomic nucleus due to mass defect. This is also why the mass of a proton or neutron by itself is more than (and not equal to) 1 u.

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Q.4
A free neutron decays into
A. A proton, a positron and a neutrino
B. A proton, a positron and a antineutrino
C. A proton, an electron and a neutrino
D. A proton, an electron, and an antineutrino
Explaination / Solution:

Free neutrons are unstable. A free neutron () decays into a proton (), an electron (), and an electron antineutrino (). This phenomenon is called beta decay.

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Q.5
Relation between atomic number (Z), neutron number (N) and mass number (A) is
A. A= Z - N
B. Z = A + 2N
C. A = Z + N
D. Z = A + N
Explaination / Solution:

mass number (A) = total number of nucleons = number of protons + number of nutrons = atomic number (Z) + neutron number (N).

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Q.6
Nuclear species or nuclides are shown by the notation ____________ where X is the chemical symbol of the species.
A. NAX
B. NZX
C. AZX
D. ANX
Explaination / Solution:

Atomic mass number (total number of nucleons) and the atomic number (number of protons) of the species are given by A and Z, respectively.

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Q.7
Contains
A. 79 protons and 118 neutrons
B. 79 neutrons and 118 protons
C. 79 protons and 197 neutrons
D. 197 protons and 118 neutrons
Explaination / Solution:

Number of protons = Atomic number = 79 Number of neutrons = Atomic mass number - atomic number = 197-79 = 118.

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Q.8
The nuclei of isotopes of a given element contain the same number of
A. Protons
B. Positrons
C. Neutrinos
D. Neutrons
Explaination / Solution:

Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of a given element have the same number of protons in each atom. Workspace
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Q.9
The nuclei of isotopes of a given element differ from each other in their number of
A. Protons
B. Neutrons
C. Positron
D. Electrons
Explaination / Solution:

Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of a given element have the same number of protons in each atom. Workspace
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Q.10
All nuclides with same mass number A are called
A. Isoclines
B. Isotopes
C. Isobars
D. Isotones