How does VSEPR help determine the shape of the molecule? A) The shape of the molecule is determined by the mass of the nuclei of different atoms in molecule, so that the mass is as evenly distributed as possible.
B) The shape of the molecule is determined by the valence electrons of the different atoms within a molecule repelling each other, so the atoms are as far apart as possible from any other valence shell.
C) The shape of the molecule is determined by the electronegativity values of the different atoms within a molecule, so the atoms are spaced apart based on decreasing electronegativity.

B) The shape of the molecule is determined by the valence electrons of the different atoms within a molecule repelling each other, so the atoms are as far apart as possible from any other valence shell.

Explanation:

VSEPR denotes Valence Electron Pair Repulsion.

It is one of the theories used to predict the model of a compound or molecule.

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.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-