Fill in the blanks with the most appropriate option:-

Try this medicine, it will prove ________.

Effective

The most appropriate option to fill in the blanks is effective.

The word "effective" means producing a desired result. In the context of the sentence, "Try this medicine, it will prove effective", the medicine is expected to produce the desired result of curing the illness. The other options are not as appropriate.

• Effectual means producing a desired result or having a significant impact. This is a more formal word than "effective", and it is not the most appropriate word to use in the sentence.
• Effectively means in an effective way. This is a adverb form of "effective", and it is not the most appropriate word to use in the sentence.
• Effectfully is not a word.