Butter and sugar being made into toffee. Is it a chemical change or a physical change? Give reason.

While making a toffee, butter and sugar is cooked. As a result, new substance called toffee is formed. This is an example of a chemical change. A chemical change generally involves the formation of a new substance, absorption or release of energy, etc.

Cotton being woven to make sheets. Is it a chemical change or a physical change? Give reason.

The process of weaving involves the joining of cotton yarns together using hand or with the help of looms. It involves the formation of no new substances with new properties. Therefore, cotton being woven to make sheets is a physical change.

Coal burning in air. Is it a chemical change or a physical change? Give reason.

Coal is a fossil fuel. When coal is burnt in air, it produces carbon dioxide. That is, it involves the formation of a new substance. Therefore, burning of coal in air is a chemical change.