12. To further describe the structure of atoms, fill in the blanks below.
Every atom consists of a central mass called the
__and a surrounding region (sometimes called the
electron cloud) that contains one or more
.The
move around the
at very high speeds. In the central mass we always find particles called
and
sometimes additional particles of equivalent mass called

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.

not always but somethings can be reproduced in a laboratory.