UPSC Combined Geo-Scientist, Mains · 2025 · Mains Paper I
Q1(i). Complete the nuclear equations
Question
Complete the following equations: ⁹₄Be + ⁴₂He → ¹²₆C + ___; ¹⁶₈O + ²₁H → ¹⁴₇N + ___; ²⁷₁₃Al + ___ → ³⁰₁₅P + ¹₀n; ²³₁₁Na + ⁴₂He → ²⁶₁₂Mg + ___; ⁴₂He + ¹⁴₇N → ___ + ¹⁷₈O
Answer in brief
Missing particles: ¹₀n, ⁴₂He (α), ⁴₂He (α), ¹₁H (p), ¹₁H (p).
Key points
- Rule: mass number A and atomic number Z are conserved on both sides.
- ⁹₄Be + ⁴₂He → ¹²₆C + ¹₀n: (α,n), discovery of neutron, Chadwick 1932.
- ²⁷₁₃Al + ⁴₂He → ³⁰₁₅P + ¹₀n: (α,n), first artificial radioisotope, Joliot-Curie 1934.
- ⁴₂He + ¹⁴₇N → ¹₁H + ¹⁷₈O: (α,p), first transmutation, Rutherford 1919.
- The paper prints the product of the third equation as 0h; read as ¹₀n (misprint).
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
Coversnuclear reactionsbalancing nuclear equationsartificial transmutationalpha particleChadwick neutron
All parts of Question 1
- 1(a) Defect in silver chloride5 marks
- 1(b) Isomerism in [(NH₃)₅CoONO]Cl₂ and [(NH₃)₅CoNO₂]Cl₂5 marks
- 1(c) Trans effect: Niᴵᴵ, Ptᴵᴵ, Pdᴵᴵ5 marks
- 1(d) Phenolphthalein in dilute and in concentrated alkali5 marks
- 1(e) Solubility product of silver chromate5 marks
- 1(f) Colour change interval of diphenylamine5 marks
- 1(g) Eriochrome Black T and calcium5 marks
- 1(h) Tendency to form metal clusters5 marks
- 1(i) Complete the nuclear equations5 marks
- 1(j) First ionisation enthalpy of 5d elements5 marks