Each of the letters in the word DIAGNOSE is arranged in alphabetical order. How many letters are there in the English alphabetical series between the letter which is third from the left and the one which is fifth from the right?

D,I,A,G,N,O,S,E

After arranging them alphabetically:

A,D,E,G,I,N,O,S

third letter from the left = E

fifth letter from the right = G

The letter F lies between E and G. Thus, there is 1 letter between them.

Thus, correct option is (c).