Question

Petrol also does not rect with sodium and potassium but y they r not kept in petrol?

Answer 1

Petrol and kerosene are coming from same source of fossil fuel. Both of them madeup of hydrocarbons. Actually sodium and potassium metals were stored in kerosene inorder to avoid the their contact with atmospheric moisture.
Not only kerosene you can use some other inorganic solvents make sure it should not contain any moisture content and especially oxygen.
Thus using petrol inplace of kersene to store sodium and potassium is not a problem. May be because of its availability and cost makes kerosene preferable over petrol.

Answer 2

Hay everybody here is the answer.Petrol and kerosene are coming from same source of fossil fuel. Both of them madeup of hydrocarbons. Actually sodium and potassium metals were stored in kerosene inorder to  avoid the their contact with atmospheric moisture.
Not only kerosene you can use some other inorganic solvents make sure it should not contain any moisture content and especially oxygen.
Thus using petrol inplace of kersene to store sodium and potassium is not a problem. May be because of its availability and cost makes kerosene preferable over petrol.