And bear in mind that sulfuric acid is only one possibility among several!

Liquid oxygen, which is also pretty easy to produce or acquire, expands quite a bit when it evaporates, and rapidly oxidizes all of your pretty organic chemistry. If you could ship enough liquid oxygen (transfigured into something else) inside a human, they would burn and explode when the transfiguration wears off.

Botulinum toxin was also mentioned in the fic and is the weapon of choice for DIY genocide.

Pyrophoric substances, transfigured and then finely ground, will start burning in an oxygen-containing atmosphere.

Obtain nuclear weapons material (the hard part) and transfigure several subcritical pieces into iron, assemble them to give one large ball, drop it (or bury it underground), and run.

Certainly not all of these are practical, but all of them sound awesome.