If a number is divisible by 55 than it must alsobe divisible by factors of 55 that is 5 and 11.

∵ 4ab5 is divisible by 11

∴ By divisibility test of 11 difference of the sum of the alternate digits must be a multiple of 11.

⇒ (4 + b) – (a + 5) = 0,11,22…

⇒ 4 + b – a – 5 = 0,11,22…

⇒ b – a -1 = 0,11,22…

⇒ b – a – 1 = 0 ( least value of b – a).

⇒ b – a = 1

Therefore option (b) is correct.