Hydrogenation of ethene represented by ,
C2H4 (g) + H2 (g) → C2H6 (g)
is an example of
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → First order reaction.
The order of a reaction is the sum of the powers of the concentration terms in the experimentally found rate law. It need not match the coefficients in the balanced equation.
For the hydrogenation of ethene, the experimental rate law contains only the concentration of ethene, to the power 1, and not that of hydrogen. So the reaction is first order, and its rate constant has the unit s−1.
NCERT (2026-27 edition):
First Order Reactions – …
