Answer:
The preposition is the word "To"
John wrote an email to his mother to ask her if he could go to the mountains.
Step-by-step explanation:
Prepositions are short words used to make connections between the clauses of a sentence, leaving the text fluid and cohesive and improving its reading and understanding. In the English language the prepositions are the words "in," "on," "at," "to" and "for.
In the case of the sentence presented above, we can see that the prepositions are the words "to" located after the word "email" and the article "the". The "to" before the verb "ask" is not considered a preposition because it is being used as an auxiliary to the verb, to indicate that this verb is in its infinitive form.