After a radioactive atom decays, it is the same element that it was before with no measurable change in mass. which kind of decay has occurred, and how do you know?
1)alpha decay because alpha particles have no mass
2)beta decay because this kind of decay cannot change one element into another 3)alpha decay because it creates a new isotope of the same element
4)gamma decay because photons have no mass

The correct answer is Option 4.

Explanation:

The types of decay processes are:

1.) Alpha decay: This decay process is defined as the process where alpha particles are emitted when a heavier nuclei decays into lighter nuclei. The alpha particle released has a charge of +2 units and mass of +4 units. The mass number of the formed nuclei gets reduced by 4 units.

2.)Beta-decay: This decay process is defined as the process in which, a neutron gets converted into a proton and an electron thus, releasing a beta-particle. The beta particle released carries a charge of -1 units. The atomic mass changes slightly because a new element is getting formed.

3.) Gamma ray emission: This decay process is defined as the process, in which an unstable nuclei gives off excess energy by a spontaneous electromagnetic process and thus releases . These radiations does not carry any charge and are electrically neutral.  The mass number of the nuclei formed remains same as that of the parent nuclei.

From the above information, the correct answer is Option 4.