Identify the missing letter in the given alphabetical series: C, E, G, I, ?

From the letters of the word 'DEPARTMENT', which of the following words CANNOT be formed? (Letters cannot be used more times than they appear).

From the letters of the word 'SIGNATURE', which of the following words CANNOT be formed? (Letters cannot be used more times than they appear).

From the letters of the word 'GOVERNMENT', which of the following words CANNOT be formed? (Letters cannot be used more times than they appear).

From the letters of the word 'CONSTRUCTION', which of the following words CANNOT be formed? (Letters cannot be used more times than they appear).

From the letters of the word 'QUALIFICATION', which of the following words CANNOT be formed? (Letters cannot be used more times than they appear).

From the letters of the word 'TEMPERATURE', which of the following words CANNOT be formed? (Letters cannot be used more times than they appear).