What are atoms?
what determines an atoms reactivity?
what determines an atoms identity?
what are valence electrons?

The smallest particle of a chemical element can be defined as an atom.

Explanation:

The number of protons in one atom of an element determines the atom's identity, and the number of electrons determines its electrical charge.

a single electron or one of two or more electrons in the outer shell of an atom that is responsible for the chemical properties of the atom is known as valence electrons.

An atom's reactivity is its tendency to lose or gain electrons. ... This is because they have one outer electron and losing it gives them the stability of a outer electron shell as the next level... The reactivities of elements can be predicted by periodic trends.

Hope this helps! :^)

Explanation:

Atoms are the basic building blocks of ordinary matter. Atoms can join together to form molecules, which in turn form most of the objects around you.

The number of protons in one atom of an element determines the atom’s identity, and the number of electrons determines its electrical charge.

Valence electrons: an electron of an atom, located in the outermost shell (valence shell) of the atom, that can be transferred to or shared with another atom.

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.

5.6⋅10−^19  j

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