[Bassel]

How is the Isopropyl named methylethyl???
        R
        |
       CH-CH3
        |
       CH3

How if we combine CH and CH3=> we will have Ethene (C2H4) and Methane (CH3)
HOW COME THEY BECOME methYL ethyl

[Archer]

C₂H₄ is the molecular formula (you are correct that it is the molecular forumla for ethene but it is also given the trivial name of ethylene when it is CH₂-CH₂), it gives no indication of structure. By your logic CH₃ should not be methane, methane is CH₄.

What you have is CHCH₃ which is a substituted ethyl group by IUPAC rules.