Is it permissible for me to give to Christians books which contain aayaat of the Quran that prove the Oneness of Allah, which are written in Arabic with the translation of the meaning written in English?
Yes, it is permissible for you to give them books containing aayaat from the Quran and to use (these quotations) to prove various issues, Tawheed and others, whether this is in Arabic or the meanings are translated. This is a deed for which you are to be commended, because giving them or lending them to them is a kind of conveying the message and calling them to Allah (da’wah). The one who does this will be rewarded if his intention is sincere.