Simplify the following text for a Grade 9 native English-speaking person.
Original: It decomposes to arsenic trioxide , elemental arsenic and iodine when heated in air at 200 Â C. The decomposition , however , commences at 100 Â C and occurs with the liberation of iodine .
Simplified: It breaks down when heated to make arsenic trioxide , arsenic metal , and iodine .