# By emitting an alpha particle, an atom of uranium-235 decays into an atom of thorium. An alpha particle, which is the same as a helium nucleus, is represented by "_2^4He. How would you complete the equation for this reaction? "_92^235U -> "_?^?He

${\text{_92^235U rarr ""_2^4He + }}_{90}^{231} T h$
I can't say that mass and charge are conserved here, because this is a nuclear reaction not a chemical one. I don't know how energy is transferred here; nor do I know the half-life of ""_92^235U. You might get a better answer in the Physics section.......