ash
mixture
Bread contain C, O, H; fillings are very different.
It consists of many different elements, often in different states. So it has bread and a least one other substance, plus some kind of spread. It may have a lot of substances in it, and could have things like salad cream in it, which is not solid.
it shrinks but preserve itself
A cheese sandwich would be a mixture because it is composed of dissimilar substances (bread and cheese).
ash
Organic materials are burned and transformed in water and carbon dioxide; the not flammable components remain as ash.
that black powder is called carbon
Foods are not pure elements; with indulgence carbonized materials as caramel, burned bread, etc. can be considered foods.
roast toast
Burned bread has not been known to cause cancer. There have been no studies supporting this seemingly bizarre medical claim.
Bread is not a change. It is a mixture of substances that can undergo physical and chemical changes.
Despite the huge amount of chemicals put into modern bread there is no move yet to call bread a chemical. Thus it has no specific chemical formula. Bread is mostly comprised of starch and cellulose, both of which are massive molecular constructs of basic sugars. Thus bread is mainly Carbon, Hydrogen and Oxygen.
wheat and grains
roast toast
roast toast
Bread crumbs are hydrocarbons since they come from bread made with wheat.