Answer: 90
Explanation:
To calculate the mass number of the missing daughter nuclei, the equation must be balanced.
The sum of the mass number in the left hand side = 1 + 235 = 236
The sum of mass number in the right hand side must be equal to 236.
Then, 236 - (143 + 3×1)
236 - ( 143 + 3)
236 - 146 = 90
