In a certain code language, “MATURE” is written as “AMUTER”, and “MENTAL” is written as “EMTNLA”. How will “MOBILE” be written in that language?

OMIBEL

Given; In a certain code language, “MATURE” is written as “AMUTER”, and “MENTAL” is written as “EMTNLA”. 

The logic followed here is;

(1st and 2nd letter interchanged their positions, 3rd and 4th interchanged their positions and 5th and 6th also interchanged and so on)

So,

that's how we get  “MATURE” is written as “AMUTER”

Similarly,

 “MOBILE” be written as OMIBEL