A

The working of an atomizer involves the conversion of liquid into a fine spray, which is achieved through a mechanism that utilizes the principles of fluid dynamics.
Step 1: Understand that an atomizer operates by creating a low-pressure region that draws the liquid up from a reservoir.
Step 2: According to Bernoulli's theorem, an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. This principle is crucial in the operation of an atomizer as it creates the necessary conditions for the liquid to be atomized.
Step 3: In an atomizer, when air passes through a narrow passage, it increases in velocity, resulting in a drop in pressure, which draws the liquid into the air stream.
Therefore, the correct answer is A: Bernoulli's theorem.