Can anyone provide the full list of noun or adjectives which starts with 不.for eg. 不可能. As it is more convenient and better way to write in Japanese rather than to mention its negative form
Using jisho.org, you can get two lists (one for nouns and another for adjectives) by leveraging search options. For each case, type into the search placeholder:
Here you are the results for nouns and for adjectives. Jisho provides lists of 747 nouns and 277 adjectives starting by 不 respectively. I think that an or operator that enables you to combine both results in a single query is not available for jisho.org, it may be for other sources. If you want a list of words that can be both nouns and adjectives at the same time, you can chain the tags in a single search:
不* #noun #adjective
This produces 252 results (see here).
Take into account that using search options in a dictionary is as exhaustive as the dictionary you use. In general, you would get a different result if you try a similar search in a different dictionary. In the case of Jisho, it uses the JMdict database of words.
You're asking for something on a similar scale to providing a full list of English words that start with "un-". There are a lot. There are a lot that probably don't show up in a dictionary but which would be understood by many Japanese people on the street.
Here is a search on WWWJDIC for words with that kanji in the initial position, which is essentially what you asked for. I tried scrolling through to see if there was any indication of how many entries there are, but the best I can say is "more than 100, even if you limit it to common words".