If 1 is added to each even digit and 1 is subtracted from each odd digit in the number 457943246 , what will be the sum of the digits that are fourth from the left and fourth from the right?

if 1 is added to each even digit and 1 is subtracted from each odd digit in the number

then modified number will be

Fourth digit from the left 8 and fourth digit from the right 2

Sum: 8+2 = 10

Thus, Option B is the correct answer.