Study the letter series given below and answer the question that follows:
$H, D, Y, S, M, W, N, B, Q, P, O, C, R, T, B, L, Z, V, E, G, U, F$
Which letter has the same neighbours as in the alphabetical order,although they have changed places?

If in the word $DISTANCE$ all the vowels are replaced by the next letter and all the consonants are replaced by the previous letter and then all the letters are arranged alphabetically,which letter will be third from the right?

How many such pairs of letters are there in the word $DOCUMENTARY$,each of which has as many letters between them in the word as there are between them in the English alphabet?

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

Each of the following questions is based on the following alphabet series.
$A, B, C, D, E, F, G, H, I, J, K, L, M$
$N, O, P, Q, R, S, T, U, V, W, X, Y, Z$
Which alphabet comes immediately before the sixth alphabet from the left extreme of the given alphabets?

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