Final answer:
The mistake in the sentence is the verb tense. It should be 'we will run' instead of 'we will ran.'
Step-by-step explanation:
The mistake in the sentence is the verb tense. Instead of saying 'we will ran,' it should be 'we will run.' In this case, 'will' is the helping verb and 'run' is the main verb.
It is important to use the correct verb tense to convey the intended meaning and to ensure grammatical accuracy in a sentence.
Corrected sentence: 'We will run tomorrow, if it isn't raining.'
Learn more about verb tense