Each vowel in the word 'ICTERID' is changed to the letter immediately following it in the English alphabetical order and each consonant is changed to the letter immediately preceding it in the English alphabetical order. How many letters will appear exactly twice in the group of letters thus formed?

Given: 'ICTERID'

Logic: Change the vowels of the word to the next immediate letter:

I$$\rightarrow$$J; E$$\rightarrow$$F; I$$\rightarrow$$J

Change the consonants of the word to the preceding immediate letter:

C$$\rightarrow$$B; T$$\rightarrow$$S; R$$\rightarrow$$Q; D$$\rightarrow$$C​

Thus, the word becomes 'J BSFQ J C'.

So, only 1 letter appears exactly twice in the group of letters formed.

Thus, the correct answer is (b).