As the electrical energy of lightning is discharged into the air,
a. the air cools and condenses rapidly.
c. the air cools and expands rapidly.
b. the air heats and condenses rapidly.
d. the air heats and expands rapidly.

d. the air heats and expands rapidly.

Explanation:  

Air is an insulator. Thus, it does not carry electrical charge. When charges accumulate in the cloud overcomes the insulation of air, lightning occurs and it discharges electrical energy which is as high as 1 billion Joules. This, huge amount of energy heats up the surrounding air and air expands rapidly. Thus, we hear thunder sound which is due to rapid expansion of air and see the lightning.

multiple

force required to detach it is given by

charges are taken to be fundamental charge

now we have

so above is the minimum distance at which it will detach