human
Which of these scenarios describe chemical reactions?
gpt
a. copper turns green on exposure to air; b. when sodium bicarbonate is combined with hydrochloric acid, bubbling is observed; d. a pure copper penny forms bubbles of a dark brown gas when dropped into nitric acid.
Explanation: Chemical reactions involve the transformation of substances and often release or absorb energy. In this case, scenarios a, b, and d all show evidence of chemical reactions through color changes, gas evolution, and other signs.