Option 1 states that smoking causes an increase in SO2 (sulfur dioxide) levels in the blood. However, this is inaccurate. While smoking can introduce various harmful substances into the body, increased SO2 levels in the blood specifically as a result of smoking is not supported.

Option 2 claims that smoking causes a decrease in O2 (oxygen) content in the blood. This is indeed correct. When a person smokes, the harmful chemicals in cigarette smoke, such as carbon monoxide (CO), bind with the oxygen-carrying molecule called hemoglobin in red blood cells, reducing its ability to transport oxygen. As a result, there is a decrease in the amount of oxygen available to body tissues, leading to oxygen deficiency.

Option 3 suggests that smoking causes an increase in CO (carbon monoxide) and CO2 (carbon dioxide) content in the blood. While smoking does lead to an increase in CO levels in the blood, it does not directly cause an increase in CO2 levels. CO2 levels in the blood are primarily regulated through respiration and not influenced by smoking.

Option 4 correctly states that smoking causes an increase in only CO content in the blood. CO is a poisonous gas that binds to hemoglobin more effectively than oxygen, reducing