Assertion (A) : All exothermic reactions are feasible at all temperature
Reason (R) : Evaporation of water can occur only at high temperature.

All exothermic reactions are spontaneous at room temperature. Whether a reaction should undergo exothermic or endothermic can be determined by its (delta)H or change of enthalpy. But whether the reaction will go spontaneous can be determined by its (delta)G or the Gibbs free energy.

Evaporation occurs regardless of the temperature because the air molecules that hit the surface provide the molecules some energy. Since a molecule's kinetic energy is proportional to temperature, greater temperatures cause more evaporation. Thus, water typically evaporates easily at that boiling point.