Explanation:

- The pattern starts with the word "BRAIN."

- The next word is "DRAIN," where the 'B' changes to 'D.'

- Then, "DTAIN," where 'R' changes to 'T.'

- The sequence follows with '?', which we will find.

- Next is "DTCKN," where 'AI' changes to 'CK.'

- Finally, "DTCKP," where 'N' changes to 'P.'

Now let's resolve the missing sequence:

- Based on the sequence, "DTAIN" should transform to a new word.

- Looking at letter changes in the series, the pattern suggests a pattern of letter increments.

- From "DTAIN," changing 'A' to 'C' forms "DTACN."

Let's match above with options:

- Option 4: DTACN is the correct replacement.

So the correct option is:

- Option 4: DTACN