`NH_(3)` and `SO_(2)` gases are being prepared at two corners of a laboratory. The gas that will be detected first in the middle of the laboratory is:

Explanation

Ammonia gas will reach first to a person in the cenre of the laboratory because it is lighter than hydrochloric acid gas. This is according to the Graham's law of diffusion which states that the rate of diffusion of a gas under given conditions of temperature and pressure is inversely proportional to the squar root of its density.