molecular energy level. (physical chemistry). One of the states of motion of nuclei and electrons in a molecule, having a definite energy, which is allowed by quantum mechanics.1  Facebook.olecular energy level. (physical chemistry). One of the states of motion of nuclei and electrons in a molecule, having a definite energy, which is allowed by quantum mechanics. 1  Facebook.
Air first enters your body through your nose or mouth, which wets and warms the air. (Cold, dry air can irritate your lungs.) The air then travels through your voice box and down your windpipe. The windpipe splits into two bronchial tubes that enter your lungs.
1 A chronic dry cough may be a sign of mild asthma. Other symptoms may include wheezing, shortness of breath, or a feeling of tightness in the chest. For more information, see the topic Asthma in Teens and Adults.  Blockage of the airway by an inhaled object, such as food or a pill.