Physics
It is easy to burst a gas-filled balloon with a needle than with a nail. It is because

Nail is more longer than needle.
Gas is reactive with the needle.
Nail exerts more pressure than needle on the balloon.
Needle exerts more pressure than nail on the balloon.

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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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