The energy absorbed or released when a neutral atom loses one electron

ionization energy

Explanation:

Ionization energy is the energy required to remove the most loosely bound electron from a gaseous atom.

Metals have low ionization energy as they tend to attain stable configuration by losing the valence electrons. Example: Sodium

Nobles gases have high ionization energy as they do not tend to lose electrons easily due to their high stability.

In a group, the ionization energy decreases as we move down as the size increases and thus the valence shell moves farther from nucleus and thus is easier to remove.

In a period, the ionization energy increases as we move across, the size decreases and thus the valence shell moves near to the nucleus and thus it gets difficult to remove.

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.

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