To what temperature must propane be cooled to remain a liquid at standard sea level?

any temperature below 40°c
any temperature above -42°c
at or below -42°c
below 20°c

At or below -42°C

Explanation:

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As propane is gaseous at the standard sea level wherein the atmospheric pressure is 1 atm and the environmental temperature roughly 25°C, in order to condense it, say convert it from gas to liquid, one must cool it down at least until its boiling temperature which is -42°C. In such manner, to remain as a liquid, it must be cooled down at or below 42°C.

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