If 1 is added to each odd digit and 2 is subtracted from each even digit in the number 3178546, what will be difference between the highest and lowest digits in the number thus formed?

Given: 3178546

Add 1 to each odd digit and subtract 2 from each even digit.

3 (odd) → 3 + 1 = 4

1 (odd) → 1 + 1 = 2

7 (odd) → 7 + 1 = 8

8 (even) → 8 − 2 = 6

5 (odd) → 5 + 1 = 6

4 (even) → 4 − 2 = 2

6 (even) → 6 − 2 = 4

New digits: 4, 2, 8, 6, 6, 2, 4

Highest digit = 8

Lowest digit = 2

Difference: 8 - 2 = 6

6 will be difference between the highest and lowest digits in the number thus formed.

Thus, correct option is (b).