Is pneumonia can happen due to over-the-counter antacids like tums (calcium carbonate) ?

No: There is possibly an increase in pneumonia in hospitalized patients taking strong acid reducers. No worry with tums (calcium carbonate).

No: Pneumonia is an infection of the lungs that can be caused by a bacteria or virus. These are microscopic pathogens that are inhaled into the lungs. Usually passed from one person who is ill through a cough and inhaled by another. Cover your mouth and nose when you sneeze or cough and wash hands often when ill!

Unlikely: Stomach acid is though to stimulate the cough reflex if stomach contents spill into the airways ("aspiration"). Prescription antacids like ppi's that eliminate stomach acid are hypothesized to cause more pneumonia in people taking them, because their cough reflex is not stimulated the same. This is not known to occur with over the counter antacids, although theoretically it could.