A) 69, 172
B) 172, 69
C) 180, 70
D) 182, 68
Correct Answer: A
Solution :
Key Idea: (i) Total mass of reactants = total mass of products (ii) When a-particle is ejected, atomic weight of atom decreases by 4 and atomic number decreases by 2. (iii) When a \[\beta \]-particle is ejected, atomic weight of atom remains same and atomic number is increased by 1. (iv) When a \[\gamma \]-particle is ejected atomic weight of atom and atomic number of atom remain same. \[\therefore \] \[_{72}{{X}^{180}}{{\xrightarrow{-2\alpha }}_{68}}{{A}^{172}}{{\xrightarrow{-\beta }}_{69}}{{B}^{172}}\] \[{{\xrightarrow{-\gamma }}_{69}}{{X}^{172}}\] \[\therefore \] \[A=171\] and \[Z=69\]
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