Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. Cigarette smoking is one of the major cause for the condition. Pneumonia is a lung disease commonly caused by the pathogen Streptococcuspneumoniae resulting in increase in lung fluid in breathing passage. Increased levels of $\mathrm{C}{\mathrm{O}}_2$ in blood leads to decreased pH caused due to the condition, respiratory acidosis where the individual is not able to exhale enough $\mathrm{C}{\mathrm{O}}_2$ . Hence, emphysema is the right choice among other choices.