Physics
A drop of liquid assumes spherical shape because:

Intermolecular forces are strong in liquids
A sphere has the least surface area for a given volume
Inter molecular forces are weak in liquids
A sphere has the largest surface area for a given volume

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Physics
A balloon filled with hydrogen will

Burst after reaching some height
Continue going upwards uninterrupted
Reach a particular height and remain floating
Reach a particular height and start coming down

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