Number of letters skipped in between adjacent letters in the series increases by one. Which of the following series observes this rule?

$A$ group of letters is given which are numbered $1, 2, 3, 4, 5$ and $6$. Below are given four alternatives containing combinations of these numbers. Select the combination of numbers so that the letters arranged accordingly form a meaningful word.
$C, E, L, S, M, U$
$1, 2, 3, 4, 5, 6$

Arrange the given names in the order in which they would occur in a telephone directory and choose the one that comes in the middle.

$A$ group of letters is given which are numbered $1, 2, 3, 4, 5$. Below are given four alternatives containing combinations of these numbers. Select the combination of numbers so that the letters arranged accordingly form a meaningful word.
$R, U, S, G, A$
$1, 2, 3, 4, 5$

If it is possible to make a meaningful word with the first,the third,the seventh and the ninth letters of the word $SEPARATION$,which of the following will be the third letter of that word? If no such word can be made,give $X$ as the answer and if more than one such word can be made,give $M$ as the answer.

Each of the following questions is based on the following alphabet series.
$A, B, C, D, E, F, G, H, I, J, K, L, M$
$N, O, P, Q, R, S, T, U, V, W, X, Y, Z$
How many $A$'s are there in the following series which are immediately followed by $B$ as well as immediately preceded by $Z$?
$A, M, B, Z, A, N, A, A, B, Z, A, B, A, Z, B, A, P, Z, A, B, A, Z, A, B$