Answer:
Hi there!
The answer to this question is the first choice: Xe 138 (top), 54 (bottom)
Because on the left side it adds up to 240 (top) and 94 (bottom)
and the right side adds up to 102 (top) and 40 (bottom)
to equal both sides, you need 138 more to get 240 on the top and 54 on the bottom to get 94. then you use the bottom number 54, to see what element it is and Xenon is the answer.
