What is the name of this molecule CH3-CH=C=CH-CH3?

Answer 1

Start by counting your carbons - 5 carbons means you will use the prefix "pent-." There are two double bonds, so this will be an alkene, specifically pentadiene. Those double bonds should be assigned positions in the 5-carbon chain, using the lowest number possible - in this case, 2,3. This molecule would be called 2,3-pentadiene, or penta-2,3-diene.