Physics
Water pipes in hilly areas often burst on a cold frosty night, because

Frost makes the pipes rusty, so they break
The material of which pipes are made contracts due to cold and so breaks
Water in the pipes freezes and on freezing water expands, so pipes break
None of these

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Physics
A drop of liquid assumes spherical shape because:

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

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