A hydrogenation reaction is carried out at 500 K. \[C{{H}_{2}}=C{{H}_{2}}+{{H}_{2}}\xrightarrow[no\,catalyst]{500k}C{{H}_{3}}-C{{H}_{3}}\] Activation energy \[-\,{{E}_{a}}\,KJ\,mo{{l}^{-1}}\] \[C{{H}_{2}}=C{{H}_{2}}+{{H}_{2}}\xrightarrow{pd,400k}C{{H}_{3}}-C{{H}_{3}}\] Activation energy = (\[{{E}_{a}}-20\]) KJ \[mo{{l}^{-1}}\] If rate remains constant, then \[{{E}_{a}}\] is

• A. \[120\text{ }kJmo{{l}^{-1}}\]  
• B. \[100\text{ }kJmo{{l}^{-1}}\]
• C. \[20kJmo{{l}^{-1}}\]   
• D. \[80\text{ }kJmo{{l}^{-1}}\]