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2081
In a hydrogen atom what will be the radius of 5th orbit if the radius of the first orbit is 0.53 Å?
A. 5.3 Å
B. 2.65 Å
C. 0.106 Å
D. 13.25 Å
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Correct Option
Explanation
r_n = n^2 r_1, so r_5 = 25 × 0.53 Å = 13.25 Å; option D is correct.
2082
The decay of a neutron inside a nucleus results in the emission of a/an
A. Alpha particle
B. Gamma rays
C. Proton
D. Electron
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Correct Option
Explanation
A neutron can decay into a proton and an electron (beta minus decay), so an electron is emitted.
2083
Which of the following has greatest binding energy per nucleon?
A. Tritium
B. Deuterium
C. Helium-4
D. Normal hydrogen
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Correct Option
Explanation
Among the listed light nuclei, helium-4 has one of the highest binding energies per nucleon, so Helium-4 is correct.
2084
The half life of a radionuclide is 77 days. Then its decay constant is
A. 0.003/day
B. 0.012/day
C. 0.006/day
D. 0.009/day
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Correct Option
Explanation
λ = ln2 / T1/2 = 0.693/77 ≈ 0.0090 per day.
2085
The ionization energy for hydrogen atom is
A. -12.6 eV
B. -19.6 eV
C. -13.6 eV
D. -11.6 eV
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Correct Option
Explanation
The ionization energy of hydrogen in its ground state is −13.6 eV.
2086
X-rays are good for imaging
A. bones
B. tendons
C. heart
D. brain
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Correct Option
Explanation
X-rays are particularly effective at imaging bones due to strong absorption contrast between bone and soft tissue.
2087
The different isotopes of an element have the same number and arrangement of extranuclear electrons, and consequently their spectra have some general structure; they are distinguished from one another by:
A. Their stability to atmosphere
B. Their different atomic masses
C. All of above
D. Their arrangements in the shells
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Correct Option
Explanation
Isotopes have identical electron arrangements and thus differ primarily in atomic mass.
2088
If the photoelectric current goes on decreasing, it means that:
A. Photoelectrons are attracted by the anode
B. Photons are attracted by the anode
C. Photoelectrons are repelled by the anode
D. Photons are repelled by the anode
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Correct Option
Explanation
A decrease in photoelectric current indicates fewer electrons reach the anode, which occurs when the anode repels photoelectrons.
2089
Particle in β-decay is
A. Neutron
B. Electron
C. Proton
D. Photon
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Correct Option
Explanation
Beta decay emits an electron (beta particle), so the particle in beta-decay is an electron.
2090
(124) The nuclei of an element having the same charge number but different mass numbers are called:
A. Isotopes
B. Isobaric
C. Isobars
D. Isomers
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Correct Option
Explanation
Nuclei with the same charge number (Z) but different mass numbers (A) are isotopes of the same element.
