We have an alkene due to the presence of a double bond in the chain. Alkenes are named by placing the ending -ene at the end of the word.
Now, to name the initial part we must count the carbons present in the molecule. We start by counting from the side closest to the double bond so that the carbon that has the double bond has the lowest possible value. Let's see how the numbering would be:
We see that the molecule has 5 carbons, so it will start with pent-, and the double bond is located at carbon number two. So the name of the molecule will be: 2-pentene
Answer: (1) 2-pentene