Explanation:

Correct Option 1: AMI
The first word is RAT and the second word is UEY.
Now, when we traverse 3 places after R in the English Alphabet series, we get the letter U. Again, when we traverse 4 places after A in the English Alphabet series, we get the letter E. Again, when we traverse 5 places after T in the English Alphabet series, we get the letter Y. Similarly,
When we traverse 3 places after U in the English Alphabet series, we get the letter X.
Again, when we traverse 4 places after E in the English Alphabet series, we get the letter I.
Again, when we traverse 5 places after Y in the English Alphabet series, we get the letter D. Thus, we get the third word.
Thus, each word in the given series is found out by,
Finding the first letter by traversing 3 places from the first letter of the previous word in the series.
Finding the second letter by traversing 4 places from the second letter of the previous word in the series. Finding the third letter by traversing 5 places from the third letter of the previous word in the series.
Thus, applying these rules, we get the unknown word as,
Traversing 3 places after X in the English Alphabets, we get, A.
Traversing 4 places after I in the English Alphabets, we get, M.
Traversing 5 places after D in the English Alphabets, we get, I. Thus, the word is AMI.
Hence, option 1 is correct.