The question about saturation of molecules is asked very often on organic chemistry exams. It is a very easy one to answer! A saturated molecule has all single bonds. An unsaturated molecule has double bonds or triple bonds.
Therefore, alkanes are always saturated while alkenes and alkynes are always unsaturated.
Saturated hydrocarbons, due to the lack of double and triple bonds, can pack very well. That is why butter is solid at room temperature (since it is made of saturated molecules they pack well and are very close to one another). Oil, such as olive oil, on the other hand is made from unsaturated hydrocarbons. Due to the double bonds, these molecules have kinks in their structure and can't pack well. This leads to oil being liquid at room temperature.
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