Can ascorbic acid exacerbate hyperacidity or heart burn or gerd?

That can happen: Vitamin C or ascorbic acid can hurt the stomach regardless of whether or not a person has gastroesophageal reflux problems. Typical "small" amounts in foods or multivitamins should be fine though. There should be no reason a normal, healthy person needs to take extra supplements of it because one's normal diet should have enough ascorbic acid. A once-a-day multivitamin with minerals is usually ok.