[Solved] Radioactivity MCQ [Free PDF] - Objective Question Answer for Radioactivity Quiz - Download Now! (2024)

1. \(_{Z - 2}^{A - 4}Y\)
2. \(_{Z - 4}^{A - 6}Y\)
3. \(_{Z}^{A - 4}X \)
4. More than one of the above
5. None of the above

Concept:

Radioactive decay:

When the n/p ratio of an atomic nucleus is high enough to make it unstable, it decays. Radioactive decay mainlyemitsα- particles, β- particles, and gamma rays.

What happenswhen anα- particle is emitted:

ZXA→Z-2XA-4+2α4

Mass number A to (A - 4) and atomic number Z to (Z - 2).

What happenswhen aβ- particle is emitted:

ZXA—→Z+1XA+-1β0

The mass numberwill remainthe same Aandatomic number Zto(Z + 1).

Calculation:

Given:

α-decay:

\(_Z^AX \rightarrow _{Z-2}^{A-4}X\;+\; _{2}^{4}α\)

1stβ-decay:

\(_{Z-2}^{A-4}X \rightarrow_{Z-1}^{A-4}X\;+\;^{0}_{-1}β\)

2nd β-decay:

\(_{Z-2}^{A-4}X \rightarrow_{Z}^{A-4}X\;+\;^{0}_{-1}β\)

Additional Information

What happenswhen γ- rays areemitted:

• Gammadecay is theemissionof energy in the form ofphotons from the nucleus of theatom.
• Gamma raysare electromagnetic waves.
• They are pure energy. They have nomassoratomic number.

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1. 4 times
2. 2 times
3. 3 times
4. More than one of the above
5. None of the above

Concept:

• Radioactivity:
  • Radioactive decay is the process by which anunstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
  • Aradioactive nucleus consists of an unstable assembly of protons and neutronswhich becomes more stable by emitting an alpha, a beta particle, or a gamma photon.
  • Atoms are radioactive if their nuclei are unstable and spontaneously (and random) emit various particles α, β, and/or γ radiations.
• Three crucial forms of Radioactivity:
  • Gamma Decay- (Photonshavinghigh energyare throw down).
  • Beta Decay-(Dischargeconsists ofElectrons).
  • Alpha Decay-(Dischargeconsists of aHelium nucleus).
• Thefollowing tableshows thelist of particleswith theirrespective features.

Explanation:

• Charge of proton = +e
• From above it is clear thatthecharge on an alpha particle is +2e.
• That represents theα particles are 2 times the charge of proton

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1. an electron
2. a proton
3. a positron
4. More than one of the above
5. None of the above

CONCEPT:

• Radioactivity:
  • Radioactive decay is the process by which anunstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
  • Aradioactive nucleus consists of an unstable assembly of protons and neutronswhich becomes more stable by emitting an alpha, a beta particle, or a gamma photon.
  • Atoms are radioactive if their nuclei are unstable and spontaneously (and random) emit various particles α, β, and/or γ radiations.
• Three crucial forms of Radioactivity:
  • Gamma Decay-(Photonshavinghigh energyare throw down).
  • Beta Decay-(Dischargeconsists ofElectrons).
  • Alpha Decay-(Dischargeconsists of aHelium nucleus).
• Thefollowing tableshows thelist of particleswith theirrespective features.

EXPLANATION:

• From above it is clear that, a beta particle is the same asan electron. Therefore option 1 is correct.

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1. A - I, B - III, C - II, D - IV, E - V
2. A - II, B - I, C - IV, D - III, E - V
3. A - I, B - II, C - III, D - IV, E - V
4. More than one of the above
5. None of the above

The correct answer isA - II, B - I, C - IV, D - III, E - V.

• Cobalt-60:
  • It a radioactiveisotopeof cobalt usedas a radiation source in many common industrial applications, such as in leveling devices and thickness gauges.
  • It is used to treat cancer.
• Potassium-40:
  • Itis a naturally occurringbeta-emitting radioactive isotope ofpotassium.
  • It is used for Geological Dating.
• Iodine-131:
  • It is a radioisotope of Iodinewith a very short half-life of 8.02 days, making it highly radioactive.
  • It is most commonly used in the treatment of hyperthyroidism i.e Thyroid therapy.
• The radioisotope Phosphorus-32 is used in leukemia therapy as well asdiagnostic purposes.
• Carbon-14 is a beta emitter radio active isotope of carbon and is used in radiocarbon dating and radiolabeling.

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1. Equal to disintegration constant
2. Reciprocal of disintegration constant
3. Directly proportional to disintegration constant
4. More than one of the above
5. None of the above

Concept:

• The half-life of a radioactive element (T1/2):Thetime intervalin which themass of a radioactive substance or the number of atoms reducedtohalf of its initial value.
• Theexpression for the half-lifeis

\({T_{\frac{1}{2}}} =\frac{ln2}{λ}= \frac{{0.693}}{λ }\)
Where λ = is the decay rate constant

• Mean life (τ):The average lifetime of all the nuclei of a particular unstable atomic species is calledmean life.

\(τ=\frac{1}{λ}\)

whereτ is mean life, and λ isradioactive decay constant

• The relation between thehalf-life and mean lifeis given by

⇒ T1/2= 0.693×τ

Explanation:

The mean life (τ ) of a radioactive substance is reciprocal of disintegration constantλ.

\(τ=\frac{1}{λ}\)

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Radioactivity Question 6

1. radioactive
2. stable
3. Isotope
4. Isobar

Radioactivity Question 6 Detailed Solution

The correct answer is Stable.

CONCEPT:

• Radioactivity:Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
  • Aradioactive nucleus consists of an unstable assembly of protons and neutronswhich becomes more stable by emitting an alpha, a beta particle, or a gamma photon.
  • Atoms are radioactive if their nuclei are unstable and spontaneously (and random) emit various particles α, β, and/or γ radiations.
• Isotopes: The atoms of an element having thesame atomic numberbut adifferent mass numberare calledisotopes. All isotopes have thesame chemical properties.
• Isobars: The nuclei which have thesame mass number (A)but a differentatomic number (Z)are calledisobars.

EXPLANATION:

U₉₂²³⁸-----→A46119+B46119

• Since the U -238 is an unstable atomic nucleus. The nucleus having an even number of protons and neutrons then that nucleus will be stable.
• After splitting into two identical parts it produced two stable nuclei because both have an even number of protons and neutrons. Hence option 2 is correct.

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Radioactivity Question 7

1. a helium nucleus
2. a hydrogen nucleus
3. a proton
4. a positron

Radioactivity Question 7 Detailed Solution

CONCEPT:

• Radioactivity:
  • Radioactive decay is the process by which anunstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
  • Aradioactive nucleus consists of an unstable assembly of protons and neutronswhich becomes more stable by emitting an alpha, a beta particle, or a gamma photon.
  • Atoms are radioactive if their nuclei are unstable and spontaneously (and random) emit various particles α, β, and/or γ radiations.
• Three crucial forms of Radioactivity:
  • Gamma Decay-(Photonshavinghigh energyare throw down).
  • Beta Decay-(Dischargeconsists ofElectrons).
  • Alpha Decay-(Dischargeconsists of aHelium nucleus).
• Thefollowing tableshows thelist of particleswith theirrespective features.

EXPLANATION:

• From above it is clear thatthe that an alpha particle consist of two proton and two neutrons and theyare tightly bound.
• An alpha-particle is identical to the nucleus of ahelium atom. Therefore option 1 is correct.

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Radioactivity Question 8

1. rocks
2. soil
3. fossils
4. buildings

Radioactivity Question 8 Detailed Solution

The correct answer is Fossils.

CONCEPT:

Radiocarbon dating:

• Italso calledcarbon-14 method wasdeveloped by the American physicist Willard F. Libbyin about1946andhas proved to be a versatiletechnique of dating fossilsandarchaeological specimensfrom500 to 50,000 years old.
• The method is widely used by Pleistocene geologists, anthropologists, archaeologists, and investigators in related fields.
• Radiocarbon dating orCarbon-14 dating method.

​Important Points

​EXPLANATION:

• Carbon-14 dating is a method ofage determinationthatdepends upon the decay to nitrogen of radiocarbon (carbon-14 isotope).
• Carbon-14 iscontinually formed in natureby the interaction of neutrons with nitrogen-14 in the Earth’s atmosphere; the neutrons required for this reaction are produced by cosmic rays interacting with the atmosphere.
• Radiocarbon present in molecules of atmospheric carbon dioxideenters the biological carbon cycle: It is absorbed from theair by green plantsand thenpassed on to animals through the food chain.
• Radiocarbondecays slowly in a living organism, and the amount lost iscontinually replenishedas long as the organism takes in air or food andonce the organism dies, however,it ceases to absorb carbon-14, so that the amount of the radiocarbon in its tissuessteadily decreases.
• Carbon-14 has ahalf-life of 5,730 ± 40 yearsi.e., half the amount of the radioisotope present at any given time will undergo spontaneous disintegration during the succeeding 5,730 years.
• Because carbon-14 decays at this constant rate,an estimate of the dateat which an organism died can be madeby measuring the amount of its residual radiocarbon.

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Radioactivity Question 9

1. 4 times
2. 2 times
3. 3 times
4. equal

Radioactivity Question 9 Detailed Solution

Concept:

• Radioactivity:
  • Radioactive decay is the process by which anunstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
  • Aradioactive nucleus consists of an unstable assembly of protons and neutronswhich becomes more stable by emitting an alpha, a beta particle, or a gamma photon.
  • Atoms are radioactive if their nuclei are unstable and spontaneously (and random) emit various particles α, β, and/or γ radiations.
• Three crucial forms of Radioactivity:
  • Gamma Decay- (Photonshavinghigh energyare throw down).
  • Beta Decay-(Dischargeconsists ofElectrons).
  • Alpha Decay-(Dischargeconsists of aHelium nucleus).
• Thefollowing tableshows thelist of particleswith theirrespective features.

Explanation:

• Charge of proton = +e
• From above it is clear thatthecharge on an alpha particle is +2e.
• That represents theα particles are 2 times the charge of proton

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Radioactivity Question 10

1. \({ }_{12}^{22} \mathrm{Mg}\)
2. \({ }_{11}^{23} \mathrm{Na}\)
3. \({ }_{10}^{23} \mathrm{Na}\)
4. \({ }_{10}^{22} \mathrm{Ne}\)

Radioactivity Question 10 Detailed Solution

CONCEPT:

Beta decay is the radioactive decay process in which the proton is transformed into a neutron or vice versa. There are two types of beta decay processes that follow;

1. Beta-Plus decay
2. Beta-Negativedecay.

1. Beta-Plus decay - In this process proton disintegrates into the neutron which results in a decrease in the atomic number of the given sample. It is written as,

\({ }_{Z}^{A} \mathrm{X}\)→\({ }_{Z-1}^{A} \mathrm{Y}\)​​ +e++ v

Here, A is the mass number, Z is the atomic number and v is the electron neutrino.

2. Beta-Negativedecay -In this process proton disintegrates into the neutron which results in an increase in the atomic number of the given sample. It is written as,

\({ }_{Z}^{A} \mathrm{X}\)→\({ }_{Z+1}^{A} \mathrm{Y}\)+e^-+\(\bar v\)

Here, A is the mass number, Z is the atomic number, and​ \(\bar v\)​ is antineutrino.

CALCULATION:

Given nuclear reaction is

\({ }_{11}^{22} \mathrm{Na}\)→ X+ e++ v

Here we can see that it is the Beta-Plus decay because we are given e⁺and v on the product side and according to the Beta-Plus decay, the proton disintegrates into the neutron which results in a decrease in the atomic number. Therefore in X the atomic number decrease we have;

As there is a decrease in Atomic Number it turns from (Z = 11 i.e. Na to Z = 10 i.e. Ne)

Following is the reaction.

\({ }_{11}^{22} \mathrm{Na}\)→\({ }_{10}^{22} \mathrm{Ne}\)+ e++ v

Therefore, X =\({ }_{10}^{22} \mathrm{Ne}\)

Hence option 4) is the correct answer.

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Radioactivity Question 11

1. Uranium
2. Radium
3. Bismith
4. Thorium

Radioactivity Question 11 Detailed Solution

The correct answer is Thorium.

• India has the world's largest reserves of Thorium.
• The known reserves of thorium in India are estimated to be between 457,000 and 508,000 tonnes.
• Kerala, Jharkhand, Bihar, Tamil Nadu, and Rajasthan are the main producers.

Key Points

• Thorium (Th)(90atomic number, 232atomic mass) is a radioactive chemical element.
• Thorium was discovered in 1828 by the Swedish chemist Jöns Jacob Berzelius.
• According to the Atomic Minerals Directorate for Exploration and Research (AMD), a constituent Unit of the Department of Atomic Energy (DAE), India has 10.70 million tonnes of Monazite which contains 9,63,000 tonnes of Thorium Oxide (ThO₂).
• The country's thorium reserves make up 25 percent of the global reserves.
• It can easily be used as a fuel to cut down on the import of Uranium from different countries.
• It is a useful nuclear reactor fuel.
• It is silvery white but turns grey or black on exposure to air.

Additional Information

• Uranium is a radioactive chemical element of the actinoid series of the periodic table.
  • Uranium was discovered in 1789 by a German chemist Martin Klaproth in the mineral called pitchblende.
  • India claims to have discovered the world's largest uranium reserves in the southern state of Andhra Pradesh.
• Radium is a silvery-white metal that does not occur free in nature.
  • Radium was discovered in 1898 by Pierre Curie, Marie Curie, and an assistantG. Bémont.
• Bismuth is hard, brittle, lustrous, and coarsely crystalline.
  • It can be distinguished from all other metals by its color-grey-white with a reddish tinge.

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Radioactivity Question 12

1. Alpha-rays
2. β- rays
3. X-rays
4. Gamma rays

Radioactivity Question 12 Detailed Solution

• Gamma raysareusedto kill cancer cells and to sterilize medical equipment and in radioactive tracers.
• As thegamma raysare strong enough to killcancercells high-poweredgamma rays are usedto killcancercells inside the body.
• X-rays areused for the checking ofbroken bones.
• Alpha-raysis used in smoke detectors.
• β-rayis used in quality control to test the thickness of an item, such as paper.

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Radioactivity Question 13

1. 1/3
2. 1/4
3. 1/8
4. 1/16

Radioactivity Question 13 Detailed Solution

Concept:

As perradioactive decay law,thetotal number of nuclei of radioactive compounds after radioactive decayin the sample is given by given equation

\(N=N_0 e^{-λ t}\)

where N is the number of nuclei of radioactive compounds after radioactive decay, N0is thenumber of nuclei of radioactive compounds initially,λ is the decay constant and t is the time of radioactive decay.

The half-life of a radioactive element (T1/2):Thetime intervalin which themass of a radioactive substance or the number of atoms reducedtohalf of its initial value.

Theexpression for the half-lifeis

\({T_{\frac{1}{2}}} = \frac{{0.693}}{\lambda }\)
Where λ = is the decay rate constant

Calculation:

Given - T = 90 days, t = 30 days

The number of half-lives (n) in 90 days is:

\(n = \frac{T}{t}=\frac{90}{30}=3 \)

As we know:

\(N=N_o(\frac{1}{2})^n\)

\( N=N_o(\frac{1}{2})^3=\frac{N_o}{8}\)

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Radioactivity Question 14

1. Nucleus
2. Electron
3. Proton
4. Neutron

Radioactivity Question 14 Detailed Solution

CONCEPT:

• Radioactivity:Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
• Aradioactive nucleus consists of an unstable assembly of protons and neutronswhich becomes more stable by emitting an alpha, a beta particle, or a gamma photon.
• Atoms are radioactive if their nuclei are unstable and spontaneously (and random) emit various particles α, β, and/or γ radiations.

EXPLANATION:

• The endresultofradioactive decayis the creation of a stable atomic nucleus. So the radioactivity is the characteristics of the Nucleus. Hence option 1 is correct.

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Radioactivity Question 15

1. Half life
2. Mean life
3. Rate of decay
4. Rate of decay and mean life

Radioactivity Question 15 Detailed Solution

CONCEPT:

Radioactivity:

• Radioactivity is a process by which thenucleus of an unstable atom loses energy by emitting radiation.
  • ​Two forces, namely theforce of repulsion that is electrostaticand thepowerful forces of attraction of the nucleus acts in the nucleus.
  • These two forces are considered extremely strong in nature.
  • Theinstability of the nucleus increases as the size of the nucleus increasesbecause the mass of the nucleus becomes a lot toconcentrate on.
  • That’s the reason why atoms of Plutonium, Uranium are extremely unstable and showradioactivity.

Law of radioactive decay:

• At any instant, the rate of decay of radioactive atoms is proportional to the number of atoms present at that instant.

\(\Rightarrow -\frac{dN}{dt}\propto N\)

\(\Rightarrow \frac{dN}{dt}= -\lambda N\)

EXPLANATION:

Law of radioactive decay:

• At any instant,the rate of decay of radioactive atoms is proportional to the number of atomspresent at that instant.

\(\Rightarrow \frac{dN}{dt}= -\lambda N\)

Half-life (t1/2):

• Half-life is the time period after which half of the quantity of the radioactive element gets decayed.
• It is given as,

\(⇒ T_{1/2}=\frac{0.693}{λ}\) -----(1)

Mean-life (τ):

• The time for which aradioactive material remains activeis defined as the mean life of the radioactive material.
• It is given as,

\(⇒ τ=\frac{1}{λ}\) -----(2)

• By equation 1 and equation 2 it is clear that the half-life and the mean-life are independent of thenumber of atoms.
• By thelaw of radioactive decay,it is clear that the rate of decay depends on thenumber of atoms. Hence, option 3 is correct.

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