Answer:
Explanation:
Please take a look at the attached picture about the general formula of beta decay and the answer.
beta decay is an atom breaking down into a new atom of another element which the atomic number is 1 larger than the original, and one electron (β particle). The mass no. of the new atom remains same as before.
138 is iodine's mass number, the atomic number of iodine is 53, referred from a periodic table. The new atom formed will be Xe, which has an atomic no. of 54.
