Which of the statements describes a chemical property?
a) iodine (a purple solid) becomes a purple gas.
b) titanium is less dense than iron.
c) sugar burns in air to form water and carbon dioxide.
d) water boils at 100 ∘c.

The answer to your question is letter c) Sugar burns in air to form water and carbon dioxide.

Explanation:

Exist two kinds of phenomena: physical and chemical

physical phenomena are when matter only changes its physical state, like evaporation, condensation, sublimation, etc.

chemical phenomena are when matter changes, react and form a new compound.

a) Iodine (a purple solid) becomes a purple gas.  This is a physical change, sublimation, this answer is wrong.

b) Titanium is less dense than iron.  Density is a physical property of matter, this answer is incorrect.

c) Sugar burns in air to form water and carbon dioxide.  Sugar in transform into water and carbon dioxide, this is the right answer.

d) Water boils at 100 ∘C. Evaporation is a physical change, the answer is wrong.

i believe the answer is a.