1.
The proton number goes down by 2 and the nucleon number by 4.
The proton number for lead is 84 - 2 = 82; the nucleon number is 210 - 4 = 206
2.
The proton number goes up by 1 and the nucleon number stays the same.
The proton number for lead is 6 + 1 = 7; the nucleon number is 14.
This element is nitrogen.
3.
a) radioactive gases - 50 %; (b) food - 12%; (c) Cosmic rays - 10%; (d) Nuclear waste - 0.1%
4. They get exposed to cosmic rays.