The correct order of heat of combustion for following alkadienes is :

For the following reactions
$$A\buildrel {700K} \over \longrightarrow {\mathop{\rm Product}\nolimits} $$
$$A\mathrel{\mathop{\kern0pt\longrightarrow} \limits_{catalyst}^{500K}} {\mathop{\rm Product}\nolimits} $$
it was found that E_a is decreased by 30 kJ/mol in the presence of catalyst.
If the rate remains unchanged, the activation energy for catalysed reaction is (Assume pre exponential factor is same):

The increasing order of basicity for the following intermediates is (from weak to strong)

The electronic configurations of bivalent europium and trivalent cerium are
(atomic number : Xe = 54, Ce = 58, Eu = 63)