The term "3 fecl2" in a balanced equation says a) that there are three iron(ii) ions and two chloride ions bonded together. b) that there are three iron(ii) ions and 6 chloride ions bonded together. c) that there are three formula units, each consisting of two chloride ions bonded to an iron(ii) ion. d) that there are three particles, each consisting of three iron atoms and 6 chlorine atoms.

Answer : The correct option is C.

Explanation :

In , 3 ions and 6 ions are present. is formed when two ions bonded to an ions.

Thus, the term in a balanced chemical equation says that there are three formula units, each consisting of two chloride ions bonded to an iron(II) ion.

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.