answer is (B)
In C, arrays are always stored in row-major form.
Formula to evaluate 2-D array's location is:----
$loc(a[i][j]) = BA + [(i-lb_1)\times NC+(j-lb_2)]\times c$
where,
$BA$ - Base Address
$NC$ - no. of columns
$c$ - memory size allocated to data type of array
$a[lb_1 \cdots ub_1] [lb_2\cdots ub_2]$
here $BA=0, NC =100, c=1, a[0.....99][0......99]$ so $lb_1=0 , lb_2=0$
$loc(a[40][50])= 0+ [ (40-0)\times 100 + (50-0)]\times 1$
$= 0+[4000+50]\times 1 = 4050$