Question

what is the missing particle?
82 35 br → ? + 0 -1 e
82 36 kr
82 35 kr
82 35 br

Explanation:

Step1: Apply mass - number conservation

In a nuclear reaction, the sum of mass - numbers on the left - hand side equals the sum on the right - hand side. The mass - number of $^{82}_{35}Br$ is 82. The mass - number of the electron $_{ - 1}^0e$ is 0. So the mass - number of the missing particle is 82.

Step2: Apply atomic - number conservation

The atomic number of $^{82}_{35}Br$ is 35. The atomic number of the electron $_{ - 1}^0e$ is - 1. Let the atomic number of the missing particle be $Z$. Then $35=Z+( - 1)$. Solving for $Z$, we get $Z = 36$.

Step3: Identify the element

The element with atomic number 36 is Kr (krypton). So the missing particle is $^{82}_{36}Kr$.

Answer:

$^{82}_{36}Kr$