Question

Ardent but unpractical reformer or scheme substitutes in one word

Answer 1

Utopian

Hope this helps.

Answer 2

Answer:

The word Utopian is an ardent but unpractical reformer or is a scheme.  It can be referred as to an excellent idea but is practically impossible (when talking about scheme)

For example: Equal distribution of wealth.

Explanation:

One-word substitution is a process which people use to replace the wordy phrase, to make a structure seem to be clearer and more organized. It is a process to make sure that the meaning of the sentence is identical but the structure is shorter.  

Therefore, one-word substitutes are used in the long run in grammar to make a sentence clearer and to make sure that the meaning of the sentence remains unchanged.