What is an atom and expailn

a particle of matter that uniquely defines a chemical element.An atom consists of a central nucleus that is usually surrounded by one or more electrons. Each electron is negatively charged. The nucleus is positively charged, and contains one or more relatively heavy particles known as protons and neutrons.

An atom is the smallest particle of an element that can take part in a chemical reaction.Atoms are so small in size that we cannot see them under the most powerful optical microscope. Their radius is measured in nanometres.Atoms usually exist in the form of molecules or ions.They are made up of 3 subatomic particles: electrons, protons, neutrons.An atom is electrically neutral.It has a nucleus which is a small positively charged part placed in the centre. It is surrounded by circular parts called orbits.

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Ithink 2 is the correct

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.