My doubt is that,if we touch a 230 volt ac line with out touching ground or neutral line (we are in air),is there occur electric shock to us?

Why are you asking this? Its important.

When I ask this Q to my clg elect profe he does not answer it corectly,so I am curious to know about it?

Assuming there is NO ground path through your shoes or other item of ANY type... you would not get shocked... but you do not have to touch ground or the return directy to get shocked or electrocuted. ANY return path will do it.. and that's why its dangerous to do.

Being completely electrically isolated is very rare in real life situations.

If you are "in air" touching an energized line(at single point), your body has zero potential difference to the source, and 230V potential difference to earth. Any contact between your body and something grounded will create a circuit through you. The better the connection, the more current will flow and the crispier you will become.

There can be situations, however, where touching the line in two places can create a potential difference between your two hands, creating current flow across your heart. So all humor aside, keep this in the realm of thought experiments.