Fill in the blank space for the given series with the correct alternative.
$66, 36, 18, (\ldots)$

Choose the correct alternative to fill in the blanks in the series: $....\,,\;....aba....\,,\;....ba.....ab$

Choose the correct alternative for the missing terms in the series: $R, M, ?, F, D, ?$

Choose the correct alternative for the missing term in the series: $ejo, tyd, ins, xch, ?$

Find out the wrong term from the given series: $8, 27, 125, 343, 1331$.

Study the following arrangement carefully and answer the question.
$O, 4, E, J, 5, T, 1, A, M, Q, 3, 8, N, I, K, 7, W, F, 6, S, 9, U, 2, Y, X$
Four of the following five are alike in a certain way based on their positions in the above arrangement and so form a group. Which is the one that does not belong to this group?