Which of these changes is a chemical change?

Examples are burning , rusting, rotting , cooking etc.

Explanation:

A  chemical change is a change accompanied by a change in the chemical composition of the substances involved. Chemical changes are irreversible changes that brings about rearrangement of the atoms of one or more substances and a change in their chemical composition. An entirely new substance is usually formed when  chemical reaction takes place.

In a chemical reaction a chemical change occur and a new product is formed .In a chemical reaction heat is usually released or absorbed from the surrounding .Examples of chemical change are burning of wood, rusting , cooking and rotting . Like the case of burning of wood you will notice that an entirely new substance is formed that is very different from the initial substances that took part in the reaction.    

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.