Correct Answer: incognito

Solution : The correct choice is the second option .

Incognito means to avoid being recognised by changing one's name or appearance. It means someone's true identity is being concealed or hidden, and thus is the appropriate one-word substitution for travelling under a name other than one’s own .

The meanings of the other options are as follows:

• Impromptu is something that is done without a plan.
• Incredible is something that is impossible to believe.
• Invisible is something that can't be seen.