Below are the results of an experiment similar to louis pasteur`s
flask sealed flask of boiled meat broth clear, no microorganisms
flask flask of boiled meat broth with an s-shaped tube clear, no microorganisms flask open flask of boiled mear broth very cloudy, many microorganisms

question a- how did the observations for flask 2 disprove spontanious generation?
question b- why do observations for flask 3 not disprove spontanious generation?

Louis Pasteur disproved the theory of spontaneous generations by suggesting swan neck experiment. He wanted to prove that life comes from pre-existing life.

Explanation:

According to spontaneous generation theory there was spontaneous generation of life forms from non-living maters on the earth. For example: they believed that frogs and flies can grow from rotting materials like mud, straw etc.

To disprove this theory Pasteur did the swan neck experiment. In flask 1 microbes did not grow because the meat was boiled to kill the microbes and then sealed which did not allow the air to enter inside. Second flask was with curved or S-shaped neck to make sure that it is not in direct contact with air. Microbes did not grow in this flask as well because pre-existing life forms are present in air which was blocked to enter by curved neck. Since the flask 3 was open to air microbe growth was observed, thus proving the point that microbe did not come from boiled meat (non living) but from air (containing pre-existing life forms).