Correct Answer: OBKO

Solution : Given:
GATE is written as AGET.

Divide the letters of the word GATE into two halves and then reverse the order of letters of both parts, to obtain the required code –
Divide the letters of the word GATE into two halves→GA / TE
Now, reverse the order of the letters of both the parts→AG / ET
So, GATE is coded as AGET.
Similarly, follow the same pattern for BOOK→
Divide the letters of the word BOOK into two halves→BO / OK
Now, reverse the order of the letters of both the parts→OB / KO

So, BOOK is written as OBKO in the code language. Hence, the third option is correct.