Sigma bond is stronger than Pi bond because of the following reasons:

- The extent of overlapping in Sigma bond is greater than in Pi bond.
- The electron density in intermolecular axis is more in Sigma bond than in Pi bond.
- There is free rotation of atom about Sigma bond but not about Pi bond.

The two vectors (say **A **and **B**) of different magnitudes cannot be combined to give zero resultant since minimum value of combination is ІA-BІ which is not zero if AB.

The three vectors **A**, **B **and **C** of different magnitudes can be zero such that they form a closed triangle, then,

** A**+**B**+**C**=0

or, **C**=-(**A**+**B**)

Hence, the sum of three vectors may be zero if vector sum of any two vectors is equal and opposite to the third vector.

__Note__: The vectors can give this result only if...

It is theoretically possible for a substance to have a negative value of cubical expansivity, which means that the substance would contract rather than expand when the temperature increases. However, it is very rare for a substance to have a negative value of cubical expansivity over a significant range of temperatures.

One example of a substance that has a negative value of cubical expansivity over a limited range of temperatures is water. Water has a positive value of cubical expansivity at...

The difference between Gram atomic mass and Gram atomic molecular are given below: