When polonium-210 emits an alpha particle, the child isotope has an atomic mass of

The child isotope has an atomic mass of 206.

Explanation:

Alpha decay : When a larger nuclei decays into smaller nuclei by releasing alpha particle. In this process, the mass number and atomic number is reduced by 4 and 2 units respectively.

General representation of an element is given as:  

where,

Z represents Atomic number

A represents Mass number

X represents the symbol of an element

General representation of alpha decay :

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