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A radioactive nucleus ‘A’ undergoes a series of decays according to the following scheme:

The mass number and atomic number of A are 180 and 72 respectively. What are these numbers for A_{4}?

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#### Solution

A has mass number as 180 and atomic number 172.

Formation of A_{1} by α-decay:

Formation of A_{2} by *β* decay:

Formation of A_{4}:

In *r*-decay, mass number and atomic number remain the same.

Thus,

Mass number of A_{4} = 172

Atomic number of A_{4} = 169

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