Which metal is stored in kerosene oil? 

Sodium belongs to group-1 elements. Thus, sodium has 1 valence electron which it can give out easily. Due to this configuration, sodium is highly reactive in nature and even reacts with moisture present in the air with the evolution of a large amount of heat. This is such a highly exothermic reaction, that it can catch fire also.

To avoid accidents and to keep sodium metal safely, it is stored in kerosene oil so that its contact with the surroundings is prohibited.

Calcium belongs to group 2 and it has a stable valence shell configuration, thus it is not highly reactive. Iron reacts with its surroundings but the reaction is not exothermic in nature, so there is not stored in kerosene.

Hence, the correct option is (A).