Balanced nuclear equation forces the alpha decay po-210

Explanation:

Your unbalanced nuclear equation is:

The main point to remember in balancing nuclear equations is that the sums of the superscripts and the subscripts must be the same on each side of the equation.  

Then

 84 = x + 2, so x =  84 - 2 =   82

210 = y + 4, so y = 210 - 4 = 206

Element 82 is lead, so the nuclear equation becomes