Excessive smoking leads to an increase in the concentration of which substance in the blood?

Assertion $(A):$ $A$ person goes to high altitude and experiences 'altitude sickness' with symptoms like breathing difficulty and heart palpitations.
Reason $(R):$ Due to low atmospheric pressure at high altitude,the body does not get sufficient oxygen.
In the light of the above statements,choose the correct answer from the options given below.

Cyanosis refers to:

Cigarette smoking causes emphysema. Give reason.

If the thoracic wall but not the lungs in man is punctured,what will be the immediate effect?

Which of the following statements is correct regarding human respiration?