Correct Answer - Option 4 : O
Following direction from the question, replacing all the vowel to the previous letter of them in English alphabet we get new word as STRRNTND replacing O and U in SURROUND.
Now simultaneously every consonant is also replaced to next letter we get new word as TTSSNTOE as we can see in the new word TTSSNTOE second from right end is O.
Hence, O is the answer.