When a radioactive isotope releases a beta particle the atomic number of the new element is

The atomic number of the new element increases by 1 unit.

Explanation:  

Beta-decay: In this process, a neutron gets converted into a proton and an electron releasing a beta-particle. The beta particle released is basically a electron with -1 charge and no mass.

General representation of an element is given as:

where,

Z represents Atomic number

A represents Mass number

X represents the symbol of an element

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