Why did the water rush into the flask when the flask was submerged in the cold water?

Question

Why did the water rush into the flask when the flask was submerged in the cold water?

Answer 1

sounds like a Charles' law exp, where the flask comes out of a boiling water bath, ( full of hot air @ 100 Celsius), & is emersed into a sink of cold water (20 C),

once in the sink, a pinch clamp is released, & water rushes into the flask, because the air in the flask has cooled. at the colder temp. the colder air molecules in the flask move slower, putting out less pressure. with the decrease in air  pressure inside the flask, the now greater pressure outside, pushes water into the flask until the pressure inside equals the pressure outside.

the air is compressed into a smaller volume as the water enters, this concentrates the cold air, allowing the more dense air to collide against a smaller suface area, increasing its pressure,... & stopping any more water from entering