Nomenclature of common naming of alkynes vs alkenes; both -ene?
The official IUPAC name for ethyl with a double bond is ethene, but this is a relatively recent change. 
Before the official name (as an exception) was ethylene. I’m not sure about propene/propylene but am fairly confident the official IUPAC name for propyl double bond is propene and not propylene. However, these compounds are often referred to with the unofficial name as per tradition. 

For alkynes, the IUPAC name is, for ethyl, the name is ethyne.    

Don’t remember to specify the location of the double/triple bond (ex: 2 - ethene)  

For alkenes, the formula is $\ce{C_nH2_{n+2}}$ and for alkynes is $\ce{C_nH_{2n}}$.