Food is primary source of energy....but energy is released when food is oxidized.

It is classified in kingdom protista

Natural resources like forests,water resources,land resources, e.t.c. Are limited and are available to us only for a short period of time.These are conventional (most of them ) and we largely dependent upon them,hence wastage of there resources may in future lead to dearth of resources....therefore there is a great need for us to conserve resources.

Take two beaker containing HCL in it.Put magnesium in one beaker and zinc in another beaker.Respective chlorides will be formed.But magnesium reacts faster than zinc hence it is more reactive