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What is the respective number of α and β-particles emitted in the following radioactive decay ²⁰⁰₉₀X → ¹⁶⁸₈₀Y?

Asked in CBSE AIPMT 1995 · Q-value, decay and conservation laws

Answer: (4) 8 and 6

Step-by-step solution

Only α emission changes the mass number, and it takes away 4 nucleons each time.

Number of α-particles: (200-168)/4=(32)/4=8.

Those 8 α-particles on their own would carry off 16 protons, taking the atomic number from 90 to 74.

The daughter actually has Z=80, so β⁻ emissions have put back 80-74=6 units of charge.

Each β⁻ raises Z by 1, so 6 β-particles are emitted: 8 and 6.

Why the other options are wrong

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