$A$ chronic disorder in which alveolar walls are damaged due to excessive cigarette smoking is

$CO$ (Carbon monoxide) is harmful because:

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.

Which of the following can cause atelectasis?

$A$ person involved in stone masonry work is likely to suffer from . . . . . . .

What is the minimum concentration and partial pressure of $CO$ in the alveoli that is dangerous to humans?