Matric Physics: Atomic and Nuclear Physics, questions with answers

Answer: C. 10 g

16 days = 2 half‑lives: 40 g → 20 g → 10 g.

Answer: A. 1/8

30 min = 3 half‑lives ⇒ (½)³ = 1/8 of the sample remains.

Answer: C. ₁H¹

Mass: A + 17 = 18 ⇒ A = 1; charge: Z + 8 = 9 ⇒ Z = 1. X is a proton ₁H¹.

Answer: C. 12.5%

3 years = 3 half‑lives: 100% → 50% → 25% → 12.5%.

Answer: D. ₁H¹

Mass numbers: A + 17 = 14 + 4 ⇒ A = 1; charge: Z + 8 = 7 + 2 ⇒ Z = 1. X = ₁H¹ (a proton).

Answer: A. C‑14

Radioactive carbon‑14 (half‑life ≈ 5730 years) is used for carbon dating.

Isotopes are atoms of the same element that have the same atomic number (number of protons) but different mass numbers (different numbers of neutrons), e.g. ₆C¹², ₆C¹³, ₆C¹⁴ or ₁H¹, ₁H², ₁H³.
Yes — isotopes have the same chemical properties because chemical behaviour depends on the number and arrangement of electrons, which is the same for all isotopes of an element. They differ only in physical properties such as mass, density and radioactivity.

Radioactivity is the spontaneous emission of radiation (α‑particles, β‑particles or γ‑rays) from the unstable nuclei of certain elements (uranium, radium, thorium) as they change into more stable nuclei.
A nucleus becomes radioactive when it is unstable — usually because it is very heavy (Z > 82) or has an unfavourable neutron‑to‑proton ratio, so the repulsive electric force between protons is not sufficiently balanced by the short‑range nuclear force. The nucleus emits particles/energy to reach a stable configuration.