The mass number of the daughter atom formed from the alpha decay of a certain radioactive atom that has 90 protons and 142 neutrons is 228.
Alpha decay of a radioactive material is the release of an alpha particle that posseses mass number of 4 and atomic number of 2.
According to this question, a certain radioactive atom that has 90 protons and 142 neutron undergoes alpha decay. This means that the mass number of the daughter atom will be as follows:
Mass number of radioactive atom = 142 + 90 = 232
Mass number of daughter atom = 232 - 4 = 228
Therefore, the mass number of the daughter atom formed from the alpha decay of a certain radioactive atom that has 90 protons and 142 neutrons is 228.
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