Question

In 2006, Soviet dissident Alexander Litvinenko was murdered when Polonium-210 was added to his tea; he died three weeks later. Polonium-210 is an alpha emitter. What other product is formed?

Answer 1

The first number is the atomic number(it's a subscript); the second is the mass number (it's a superscript).

84Po210 = 2He4 + 82X206
Note the subscripts add up on each side; i.e., 94 = 82 + 2 and the superscripts add up. That is 210 = 26 + 4.
So X must be Pb.