Nuclear & Radioactivity — Set 1

Correct Answer: D. Spontaneous emission of radiation from an unstable nucleus

Option D is correct because an unstable nucleus emits radiation on its own. This process is a nuclear change, not a chemical change. The rate of decay is not controlled by temperature or pressure in basic cases.

Correct Answer: B. Protons

Option B is correct because atomic number equals the number of protons in the nucleus. It uniquely identifies the element in chemistry and physics. In a neutral atom, electrons equal protons.

Correct Answer: C. Same atomic number but different mass numbers

Option C is correct because isotopes have the same atomic number but different mass numbers. They have the same number of protons but different numbers of neutrons. Many isotopes are stable while some are radioactive.

Correct Answer: D. Nuclear binding energy

Option D is correct because mass defect is converted into binding energy. A nucleus has slightly less mass than its separated nucleons. The relation E = mc^2 connects mass loss to energy.

Correct Answer: C. Becquerel (Bq)

Option C is correct because becquerel means one decay per second. Activity measures how fast nuclei are disintegrating. Curie is an older non-SI unit of activity.

Correct Answer: B. 3.7 × 10^10 Bq

Option B is correct because 1 Ci corresponds to about 3.7 × 10^10 decays per second. It was based on the activity of radium-226 historically. In SI, activity is expressed in becquerel.

Correct Answer: D. A helium nucleus (2 protons and 2 neutrons)

Option D is correct because an alpha particle is the nucleus of helium-4. It carries a +2 charge due to two protons. Alpha emission reduces mass number by 4 and atomic number by 2.

Correct Answer: B. An electron emitted from the nucleus

Option B is correct because beta minus radiation is an electron emitted during nuclear change. It occurs when a neutron converts into a proton inside the nucleus. Beta particles are more penetrating than alpha particles.

Correct Answer: C. High-energy electromagnetic waves

Option C is correct because gamma rays are electromagnetic radiation of very high energy. They have no charge and travel at the speed of light in vacuum. Gamma emission often follows alpha or beta decay.

Correct Answer: D. Gamma radiation

Option D is correct because gamma rays penetrate matter the most among common nuclear radiations. Alpha particles are stopped easily and beta particles are moderately penetrating. Denser shielding like lead is often used for gamma rays.