is air gap is required for external cladding ?

Yes it is required for external cladding

It depends on the kind of cladding. Some materials, like stones, need to be attached directly on the building envelope. Some curtain-wall use the total room space as air gap. And a few synthetic cladding can be placed with a more or less ample gap, calculated after the heat of the direct sun impact on the building, across the sun yearly track.  

No, but it's much better when there is one for the airflow that prevents building overheating. 

sure

Leave a ventilation gap of 22 to 25 mm behind the cladding 

Yes Because it gives you the capability to install thermal insulation and gives you good chance to level the cladding to be vertical without being stopped by any imperfections in the concrete or the block works   

Air gap is not required but there will be created a gap between the two panel of cladding that will be filled by backing roads and sealant.

Because air Condition are most important .

Its Depends Types of the Cladding.

 

No need to take air gap in external cladding