Which half-cell reaction would have the greatest tendency to occur at the cathode?

The correct answer is the second.

Explanation:

Oxidation occurs when an element loses electrons, acquiring a positive charge. Reduction occurs when an element gains electrons and goes from a positively charged state to a neutral one.

Aluminum metal (Al) oxidizes, so we say that Al is the reducing species, which acts by reducing . Copper () is reduced, so it is the oxidizing agent, it acts oxidizing to Cu.

oxidizes to Cu, and Al reduces to .

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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.