Isotopes

Isotopes of an element have the same:
a) Mass number
b) Number of protons
c) Number of neutrons
d) Atomic mass
✅ b) Number of protons
Explanation: Isotopes differ in neutrons but share the same proton number (atomic number).
(BPSC 60th Prelims)
Which isotope is used in the treatment of cancer?
a) C-14
b) I-131
c) U-235
d) H-2
✅ b) I-131
Explanation: Iodine-131 is used in radiotherapy for thyroid cancer.
(BPSC Teacher 2023)
Deuterium is an isotope of:
a) Helium
b) Oxygen
c) Hydrogen
d) Nitrogen
✅ c) Hydrogen
Explanation: Deuterium (H-2) is hydrogen with one neutron.
(CDPO 2017)
Which isotope is used for carbon dating?
a) C-12
b) C-14
c) O-16
d) N-15
✅ b) C-14
Explanation: Radioactive carbon-14 helps determine the age of organic materials.
(BPSC 64th Prelims)
Isotopes of uranium used in nuclear reactors include:
a) U-235 and U-238
b) U-233 and U-235
c) U-234 and U-235
d) All of the above
✅ d) All of the above
Explanation: Multiple uranium isotopes are used in fission reactions.
(BPSC 68th)
Tritium is an isotope of:
a) Oxygen
b) Nitrogen
c) Hydrogen
d) Helium
✅ c) Hydrogen
Explanation: Tritium (H-3) has 1 proton and 2 neutrons.
(BPSC Teacher 2022)
Atomic number of isotopes remains:
a) Different
b) Same
c) Doubled
d) Zero
✅ b) Same
Explanation: All isotopes of an element have identical atomic numbers.
(BPSC Assistant 2019)
Which of the following isotopes is stable?
a) C-14
b) U-235
c) H-1
d) I-131
✅ c) H-1
Explanation: Protium (hydrogen-1) is stable and non-radioactive.
(BPSC 67th Prelims)
Which isotope is used in locating brain tumors?
a) Co-60
b) I-131
c) Tc-99
d) C-14
✅ c) Tc-99
Explanation: Technetium-99 is a diagnostic tracer in nuclear medicine.
(CDPO 2016)
Isotopes differ in:
a) Atomic number
b) Number of protons
c) Number of electrons
d) Mass number
✅ d) Mass number
Explanation: They differ due to varying number of neutrons.

NCERT-Based MCQs (Q11–30)

Isotopes have different:
a) Physical properties
b) Chemical properties
c) Atomic number
d) Electron configurations
✅ a) Physical properties
Explanation: Mass affects physical properties like density and boiling point.
Isotopes of chlorine are:
a) Cl-35 and Cl-37
b) Cl-36 and Cl-38
c) Cl-34 and Cl-36
d) Cl-33 and Cl-35
✅ a) Cl-35 and Cl-37
Explanation: These are naturally occurring stable isotopes of chlorine.
Which of the following is not an isotope of hydrogen?
a) Protium
b) Deuterium
c) Tritium
d) Helium
✅ d) Helium
Explanation: Helium is a different element, not an isotope of hydrogen.
What causes the difference in isotope mass?
a) Proton number
b) Electron number
c) Neutron number
d) Ion charge
✅ c) Neutron number
Explanation: Mass difference arises from differing neutron counts.
Medical imaging often uses:
a) Stable isotopes
b) Radioisotopes
c) Noble gases
d) Alkali metals
✅ b) Radioisotopes
Explanation: Their radiation helps visualize organs and diagnose conditions.
Which isotope is used for sterilizing surgical instruments?
a) Co-60
b) I-131
c) C-14
d) U-238
✅ a) Co-60
Explanation: Cobalt-60 emits gamma rays used for sterilization.
Which isotopes are used as nuclear fuel?
a) C-14
b) U-235 and Pu-239
c) Cl-35
d) Tc-99
✅ b) U-235 and Pu-239
Explanation: These are fissionable materials in nuclear reactors.
The number of neutrons in C-14 is:
a) 12
b) 6
c) 8
d) 14
✅ c) 8
Explanation: 14 (mass) – 6 (atomic number) = 8 neutrons.
Isotopes have identical:
a) Mass
b) Physical properties
c) Chemical behavior
d) Reactivity
✅ c) Chemical behavior
Explanation: Because their electron configuration remains the same.
Radioisotopes are useful in:
a) Photosynthesis
b) Fuel cells
c) Tracers in medicine
d) Glass manufacturing
✅ c) Tracers in medicine
Explanation: Used for diagnosis and treatment.
Which isotope is artificially made?
a) U-235
b) C-14
c) Cl-37
d) O-16
✅ b) C-14
Explanation: It is formed in upper atmosphere via cosmic rays.
The isotope of hydrogen with one proton and one neutron is:
a) Protium
b) Tritium
c) Deuterium
d) Hydrogen ion
✅ c) Deuterium
Explanation: H-2 has 1 proton + 1 neutron.
Which of these is an isotope of carbon?
a) C-12
b) C-14
c) Both
d) None
✅ c) Both
Explanation: They have 6 protons but different neutrons.
What is the mass number of a carbon isotope with 7 neutrons?
a) 13
b) 14
c) 12
d) 10
✅ a) 13
Explanation: 6 (protons) + 7 (neutrons) = 13.
Which of the following statements is false?
a) Isotopes differ in mass
b) Isotopes have same atomic number
c) Isotopes have same number of neutrons
d) Isotopes behave similarly chemically
✅ c) Isotopes have same number of neutrons
Explanation: They differ by neutron count.
Which of these is a radioactive isotope?
a) Cl-35
b) U-238
c) O-16
d) H-1
✅ b) U-238
Explanation: U-238 is unstable and undergoes decay.
Stable isotopes are used in:
a) Fossil fuel testing
b) Biochemical tracer studies
c) Cooking
d) Plastic production
✅ b) Biochemical tracer studies
Explanation: They help in metabolic research.
The atomic number of isotopes of the same element is:
a) Variable
b) Same
c) Doubled
d) Zero
✅ b) Same
Explanation: Atomic number defines the element.
Isotopes of oxygen are:
a) O-14, O-15, O-16
b) O-15, O-16, O-18
c) O-14, O-17, O-18
d) O-16, O-17, O-18
✅ d) O-16, O-17, O-18
Explanation: These occur naturally.
The use of C-14 dating is limited to materials:
a) Below 500 years
b) Up to 5000 years
c) Up to 50,000 years
d) More than 1 million years
✅ c) Up to 50,000 years
Explanation: C-14 has a half-life of 5730 years, suitable for archaeological dating.
Which isotope is used in radiocarbon dating?
a) C-12
b) C-14
c) N-14
d) O-16
✅ b) C-14
Explanation: Carbon-14 is radioactive and is used to date ancient organic materials.
What is the isotope of uranium primarily used in nuclear bombs?
a) U-238
b) U-233
c) U-235
d) Pu-239
✅ c) U-235
Explanation: U-235 is highly fissionable and is the main isotope in nuclear weapons.
The term "isotope" was coined by:
a) John Dalton
b) J.J. Thomson
c) Frederick Soddy
d) Rutherford
✅ c) Frederick Soddy
Explanation: He introduced the term in 1913 while studying radioactive elements.
Which isotope is used in smoke detectors?
a) C-14
b) Am-241
c) U-235
d) H-3
✅ b) Am-241
Explanation: Americium-241 emits alpha particles used in ionization-type smoke alarms.
Tritium emits which radiation?
a) Alpha
b) Beta
c) Gamma
d) Neutron
✅ b) Beta
Explanation: Tritium is a weak beta emitter, used in self-luminous devices.
The number of isotopes of hydrogen is:
a) 1
b) 2
c) 3
d) 4
✅ c) 3
Explanation: Hydrogen has Protium (H-1), Deuterium (H-2), and Tritium (H-3).
What differentiates isotopes of the same element?
a) Electron number
b) Atomic number
c) Neutron number
d) Valency
✅ c) Neutron number
Explanation: Isotopes vary in neutron count, altering their mass number.
Medical isotopes should ideally have:
a) Long half-lives
b) Short half-lives
c) No radiation
d) High melting point
✅ b) Short half-lives
Explanation: To minimize patient exposure after diagnostic use.
The half-life of C-14 is approximately:
a) 500 years
b) 5,730 years
c) 10,000 years
d) 1,000 years
✅ b) 5,730 years
Explanation: This makes it suitable for dating specimens up to 50,000 years old.
Which isotope of hydrogen is radioactive?
a) Protium
b) Deuterium
c) Tritium
d) None
✅ c) Tritium
Explanation: H-3 is unstable and emits beta radiation.
Isotopes have:
a) Same mass number
b) Same atomic number
c) Different atomic number
d) No electrons
✅ b) Same atomic number
Explanation: They are atoms of the same element.
Which isotope is used in PET scans?
a) C-12
b) O-16
c) F-18
d) I-131
✅ c) F-18
Explanation: Fluorine-18 is a positron emitter used in PET (Positron Emission Tomography).
Uranium-238 undergoes decay to become:
a) Thorium
b) Radon
c) Lead-206
d) Carbon
✅ c) Lead-206
Explanation: It goes through multiple decays before stabilizing as lead.
Which is the most abundant isotope of carbon?
a) C-12
b) C-13
c) C-14
d) C-10
✅ a) C-12
Explanation: About 98.9% of natural carbon is C-12.
The isotope used in nuclear submarines for energy:
a) U-238
b) Pu-239
c) H-3
d) I-131
✅ b) Pu-239
Explanation: Plutonium-239 is compact and ideal for naval nuclear reactors.
Isotopes are represented by:
a) Same symbol with different atomic numbers
b) Same symbol with different mass numbers
c) Different symbols with same atomic numbers
d) None of the above
✅ b) Same symbol with different mass numbers
Explanation: Example: U-235, U-238.
Radioactive isotopes disintegrate to become:
a) Stable elements
b) Metals
c) Ions
d) Alloys
✅ a) Stable elements
Explanation: After a series of decays, they reach a non-radioactive stable state.
Which of these has three isotopes naturally?
a) Oxygen
b) Nitrogen
c) Hydrogen
d) Sodium
✅ c) Hydrogen
Explanation: Protium, Deuterium, Tritium.
Which of the following is an application of isotopes?
a) Preserving food
b) Diagnosing diseases
c) Manufacturing cement
d) Glass making
✅ b) Diagnosing diseases
Explanation: Radioisotopes are used in nuclear medicine for imaging.
Which of the following isotopes is used in thyroid imaging?
a) Co-60
b) F-18
c) I-123
d) C-14
✅ c) I-123
Explanation: Iodine-123 is safer than I-131 and is widely used for thyroid scans.