Question

210 210
Pb --> Bi + ?
82 83


60 0
Co --> ? + e
27 -1


I need an explanation on how to find the missing product.

Answer 1

The subscripts must add up on both sides. The superscripts must add up on both sides. For the first one, You start with Pb-210 and end with Bi=210; therefore, the ? particle must have a mass of zero since 210 + 0 on the right = 210 on the left. For the atomic number, you have 82Pb on the left and 83Bi on the right. Therefore, the ? particle must be -1 because 83 + (-1) = 82.
Now, what particle has a mass of zero and a charge of -1? Must be an electron. You replace ? with _-1e^o