The balanced equation will be:
Cu + 2 AgNO3 ----> 2Ag + Cu(NO3)2
The balancing of equation is done to satisfy the law of conservation of mass. This law states - "mass can neither be created, nor be destroyed". Thus, the mass of the element in the equation cannot be created or destroyed, it is just shifted.
The answer is 1,2,2,1; the first option.