In a certain code language, 'DISK' is written as 'SIKD', and 'MINE' is written as 'NIEM'. How will 'BOLD' be written in that language?

LODB

The same logic is followed;

(the 1st letter is interchanged with 5th, 2nd with 2nd, 3rd with 1st and 5th with 1st)

That' how DISK' is written as 'SIKD'

And, 

 'MINE' is written as 'NIEM'.

Similarly,

BOLD be written as LODB