The digit in the unit's place of the number (67)25 - 1 must be -

Answer: Option B

Unit digit of (67)²⁵ = Unit digit of 7²⁵
Unit digit of 7⁴ is 1 and so the unit digit of (7⁴)⁶ is 1
∴ Unit digit of 7²⁵ = (1 × 7) = 7
Hence, the unit digit of (7²⁵ - 1) is (7 - 1) = 6