What is Wrong with this name? (hint-draw the molecule out first) 3-butene
The correct IUPAC name is but-1-ene.
The structure of the compound would be
You started numbering from the wrong end.
You must number the carbon atoms from the end closest to the double bond.
The PIN (Preferred IUPAC Name) is but-1-ene.
A name like 1-butene is acceptable, but the PIN puts the locant as close to its functional group as possible.