Question

C2H4 + H2 =? ( substitution reaction)

Answer 1

Substitution reaction cannot take place.
Only addition reaction can take place here
Substitution here won't make a sense, cause you remove hydrogen and add new ones,so obviously your ethene molecule isn't a car that needs it's tyres to be changed ｡◕‿◕｡
So, yeah hope this helps you!
Addition can take in prescence of Platinum and Palladium as adsorbing catalyst to finally give ethane.

Answer 2

Here ' R ' is ' H '

This is a type of addition reaction and not substitution.

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