ii)Transition metals and their compounds show catalytic activities because of Variable or multiple oxidation states, ability to form complexes, they provide large surface area for adsorption.

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

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

In benzene molecule, carbon and carbon bond can't have polarity because there is not any electronegativity difference and the carbon hydrogen is also not much polar because the electronegativity difference is almost zero and also the small pull due to small difference in Electronegativity is balanced due to even pull from all directions.

In chlorobenzene the electronegativity difference between carbon and chlorine is very high so, it is polar.

(to compare polarity first check electronegativity...

Yes, a physical quantity can have magnitude and direction but still be a scalar if it doesn't obey the vector addition. An example is Electric Current which has magnitude and a fixed direction, but it does not follow vector laws of addition.