Atomic Masses & Nuclear Composition Challenge
25 NEET-standard questions on nuclear size, the atomic mass unit, isotopes and average atomic mass, the neutron, and Z, N and A. Answer each one. If you get it wrong, Vidya Ma’am explains it with an animated movie you can control, a slider to play with, and a step-by-step solution. Then try again.
NCERT Physics XII Part II · Ch. 13 · pp. 306–308Keys: A–D or 1–4 to answer
🧠 Formula memory tricks (open before you start)
Sizer(nucleus) ≈ r(atom) / 10⁴volume ratio ≈ 10⁻¹²; over 99.9% of the mass is in the nucleus
Atomic mass unit1 u = ¹²C mass ÷ 12 = 1.66×10⁻²⁷ kg¹²C is exactly 12 u
Particle massesmp = 1.00727 u · mn = 1.00866 uH atom 1.00783 u; electron 0.00055 u
Average atomic massM = Σ (abundance × mass) / 100chlorine: 35.47 u from 34.98 u and 36.98 u
CompositionA = Z + NZ protons, N neutrons, A nucleons. N = A − Z
Three relativesIsotopes: same Z · Isobars: same A · Isotones: same Nisotopes have the same chemistry
NeutronChadwick 1932: Be + α. Free neutron decays in about 1000 s; stable inside a nucleus.
right first tryfixed after explanationstill to fix
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