Why can you blow bubbles with soapy water but not plain water?

Answer: Soap reduces surface tension, letting water form thin films

Soap reduces surface tension, letting water form thin films ✓ — Correct! Plain water has high surface tension—water molecules pull so strongly on each other that a thin film immediately snaps back together. Soap molecules wedge between water molecules and weaken their grip on each other. This lets the water stretch into a thin, flexible film that can wrap around air. Each soap molecule has one end that loves water and one that hates it, so they line up at the surface and stabilize the film.

Soap produces gas that inflates the bubbles — Wrong. Soap doesn't produce any gas. The air inside bubbles comes from your breath or from mixing air in when you shake the water. Soap's job is to make the water film stretchy enough to hold that air.

Soap makes water lighter so it floats as bubbles — Wrong. Soap doesn't change water's weight in any meaningful way. Bubbles float because the air inside is lighter than the surrounding air, not because of weight changes in the water film.