Loop invariant is a condition which is true in every iteration.
So lets take an example say n = 123 where d1=1,d2=2,d3=3
Iteration 1 : rev = 3 n = 12 or rev = d3 and n = d1d2
Iteration 2: rev = 32 n = 1 or rev = d3d2 and n = d1
Iteration 3: rev = 321 n = 0 or rev=d3d2d1 and n=d0
So in general we are getting n = d1d2...dm-i and rev = dmdm-1.....dm-i+1 in every iteration. So option A is true.n=d1d2…dm−i and rev=dmdm−1…dm−i+1