Answer
The quarks are converted to energy.
Work Step by Step
The up quark and the anti-up quark that comprise the neutral pion annihilate each other and are converted completely to energy, in the form of photons.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.