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 is the only letter that occurs twice?

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

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.

Arrange the given words in the sequence in which they occur in the dictionary and then choose the correct sequence.
$1.$ Dissipate $2.$ Dissuade $3.$ Disseminate $4.$ Distract $5.$ Dissociate $6.$ Dissect

If it is possible to make a meaningful word with the fourth,the eighth and the tenth letters of the word $COUNTERACT$,which of the following will be the last letter of that word? If no such word can be made,give $X$ as the answer. If more than one such word can be made,give $M$ as the answer.

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