Isotopes of an element have the same number of protons but different numbers of neutrons.
Correct Answer
True
True. The number of protons fixes the element, while the number of neutrons can vary, giving isotopes with different mass numbers, such as carbon-12 and carbon-14.
Category: Nuclear Stability
Question 2
Nuclear reactions involve much smaller energy changes than ordinary chemical reactions.
Correct Answer
False
False. Nuclear reactions release or absorb energies millions of times larger per atom than chemical reactions, because they convert a measurable amount of mass into energy according to E = mc2.
Category: Nuclear Stability
Question 3
Stable nuclides with even numbers of both protons and neutrons are much more common than stable nuclides with odd numbers of both.
Correct Answer
True
True. Nucleons are more stable when paired, so most stable nuclides have even numbers of protons and neutrons, and very few have odd numbers of both.
Category: Nuclear Stability
Question 4
Nuclides with atomic numbers greater than 83 are stable.
Correct Answer
False
False. Every nuclide with an atomic number greater than 83 is radioactive. Many of these heavy nuclides decay by emitting alpha particles.
Category: Nuclear Stability
Question 5
In a balanced nuclear equation, the sum of the mass numbers and the sum of the atomic numbers are the same on both sides.
Correct Answer
True
True. Nucleons and charge are both conserved in nuclear reactions, so mass numbers and atomic numbers must each balance, which is how unknown products are identified.
Category: Nuclear Equations
Question 6
An alpha particle consists of two protons and two electrons.
Correct Answer
False
False. An alpha particle consists of two protons and two neutrons. It is a helium-4 nucleus with a charge of 2+.
Category: Nuclear Equations
Question 7
Gamma emission changes neither the atomic number nor the mass number of a nucleus.
Correct Answer
True
True. A gamma ray is a photon with no mass and no charge, so emitting one only lowers the energy of the nucleus; it often accompanies alpha or beta decay.
Category: Nuclear Equations
Question 8
Electron capture increases the atomic number of a nucleus by one.
Correct Answer
False
False. In electron capture, an inner electron combines with a proton to form a neutron, so the atomic number decreases by one and the mass number stays the same.
Category: Radioactive Decay
Question 9
Radioactive decay follows first-order kinetics, so the half-life of an isotope does not depend on how much of it is present.
Correct Answer
True
True. For a first-order process the half-life is constant, so the same fraction of the remaining nuclei decays in each half-life whether the sample is large or small.
Category: Radioactive Decay
Question 10
After two half-lives, one-quarter of a radioactive sample has decayed.
Correct Answer
False
False. After two half-lives, one-quarter of the sample remains, which means three-quarters has decayed.
Category: Radioactive Decay
Question 11
The fusion of hydrogen nuclei into helium releases the energy that powers the Sun.
Correct Answer
True
True. In the Sun's core, extremely high temperatures allow light nuclei to overcome their repulsion and fuse, converting a small amount of mass into a large amount of energy.
Category: Fission and Fusion
Question 12
Because radon is less dense than air, it tends to collect in the upper floors of buildings.
Correct Answer
False
False. Radon is much denser than air, so after seeping out of soil and rock it tends to collect in basements and lower floors. It is a leading cause of lung cancer.
Category: Radiation Effects
Question 13
In a nuclear reactor, some uranium-238 absorbs neutrons and, after two beta decays, becomes plutonium-239.
Correct Answer
True
True. Uranium-238 absorbs a neutron to become uranium-239, which beta decays to neptunium-239 and then to plutonium-239. This is how most plutonium is produced.
Category: Fission and Fusion
Question 14
A fission chain reaction is sustained because each fission event absorbs more neutrons than it releases.
Correct Answer
False
False. Each fission absorbs one neutron but releases two or three, and those neutrons can cause further fissions, which keeps the chain reaction going.
Category: Fission and Fusion
Question 15
Carbon-14 dating works because a living organism keeps a nearly constant ratio of carbon-14 to carbon-12 until it dies.
Correct Answer
True
True. Living things keep taking in carbon from their surroundings. After death no new carbon-14 is taken in, so the ratio falls as the carbon-14 decays, and the age can be calculated.
Category: Uses of Radioisotopes
Question 16
Cobalt-60 sources used in cancer radiation therapy emit alpha particles.
Correct Answer
False
False. Cobalt-60 is used in radiation therapy for the gamma rays it emits, which can penetrate the body to reach a tumor. Alpha particles would not get past the skin.
Category: Uses of Radioisotopes
Question 17
Iodine-131 is used to treat thyroid disorders because the thyroid gland concentrates iodine.
Correct Answer
True
True. The thyroid takes up iodine to make its hormones, so radioactive iodine-131 delivers its radiation to thyroid tissue in conditions such as Graves' disease.
Category: Uses of Radioisotopes
Question 18
Irradiating food with gamma rays to kill microorganisms makes the food itself radioactive.
Correct Answer
False
False. Gamma irradiation kills bacteria and other microbes that cause spoilage, but it does not make the food radioactive.
Category: Uses of Radioisotopes
Question 19
Ionizing radiation can damage cells by breaking bonds in DNA or by producing reactive free radicals from water.
Correct Answer
True
True. Radiation can harm biomolecules directly, or indirectly by ionizing water to form species such as the hydroxyl radical, which then attacks DNA, proteins and enzymes.
Category: Radiation Effects
Question 20
A dose measured in sieverts is independent of the type of radiation that delivered it.
Correct Answer
False
False. The sievert is a biologically effective dose that multiplies the absorbed dose by a factor for the type of radiation, so 1 Gy of alpha radiation counts as far more sieverts than 1 Gy of gamma radiation.
Category: Radiation Effects