Option 1 -> "In time" means with time to spare before a deadline, but doesn't work with "expected to arrive" in this context.
Option 2 -> "On time" is the correct idiomatic expression meaning punctually or at the scheduled time.
Option 3 -> "At time" is not a valid English phrase or collocation.
Option 4 -> "By time" is grammatically incorrect in this context and not a standard expression.
Hence, Option 2: on -> "On time" is the fixed expression used to indicate that something happens at the scheduled or expected time, making it the appropriate choice for describing a train's punctual arrival -> correct