Thorium-232 is a β⁻ emitter.
General decay equation for β⁻ is:
From the periodic table we can find the proton number (Z) for Thorium, it is 90.
For Thorium-232 the equation is:
Now we need to find the element that Thorium decays into (i.e. the daughter element). We just calculated (by balancing the equation above) that the proton number for the new element is 91. Look that up on the periodic table and we find that it is protactinium (Pa) so we can complete the equation: