According to the question,

Karan beats Arjun by 10 mts.

That is

Arjun runs 90mts in the same time interval (t) in which Karan runs 100 mts.

Therefore,

Applying the same data in Second case,

Both of them would be at 10 mts from the end point at the end of time interval t.

So, in time interval (t/10) , Arjun will run 9 mts while Karan will run 10 mts .

Therefore,Karan will have completed the race by beating Arjun by 1meter

Thus,Option (4) is correct.

Hope U got it clear