My dentist wants to give me nitrous oxide when I have multiple extractions I have asthma would this be ok /safe.?

Asthma and Nitrous. In over 40 years of dental practice, I have neither had a problem with a patient who had asthma nor a physician who advised against using nitrous oxide\oxygen analgesia for tooth extractions. In fact, as this relaxes you and you get more oxygen than in room air, it probably reduces any risks. However, you and your dentist should discuss this with the physician who treats you for asthma.
See specialist. Because of your medical history evaluation by an oral and maxillofacial surgeon would be prudent.
Not really. If you do not want nitrous do not get it it has nothing to do with pain it will reduce your anxiety possibly.