Number of letters skipped in between adjacent letters in the series are multiples of $3.$ 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.
$C, E, L, S, M, U$
$1, 2, 3, 4, 5, 6$

Find which one word cannot be made from the letters of the given word: $DEPARTMENT$.

Arrange the given words in alphabetical order and choose the one that comes first.

If it is possible to make only one meaningful word from the first,the third,the fifth,and the eighth letters of the word $ENTERPRISE$ using each letter only once,the first letter of that word is your answer. If more than one such word can be made,your answer is $'X'$. If no such word can be made,your answer is $'Y'$.

$A$ meaningful word is formed if we take the first,fourth,fifth,seventh,tenth,eleventh,and twelfth letters of the word $FELICITATIONS$. Which of the following will be the fifth letter of that word from the right end?