The solutions in which the electrodes are immersed are called electrolytes. The chemical reaction that takes placein a galvanic cell is the redox reaction. One electrode acts as anode in whichoxidation takes place and the other acts as the cathode in which reductiontakes place.the half-cell occurs is called reduction half-cell and the reaction taking place in it is called reduction half-cell reaction. The electrode where oxidation occurs is called anode and the electrode where reduction occurs is termed cathode. Electrons flow from anode to cathode in the external circuit.

The standard potential of hydrogen electrode is assumed to be zero at all temperature.

The Standard hydrogen electrode (abbreviated SHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. Its absolute electrode potential is estimated to be 4.44 ± 0.02 V at 25 °C, but to form a basis for comparison with all other electrode reactions, hydrogen's standard electrode potential (E⁰) is declared to be zero volts at all temperatures.

Reduction potential of fe is more than that of cr, so fe will reduce and act as cathode and cr will act as anode. now emf of cell is reduction potential of cathode - reduction potential of anode. so EMF= -0.45-(-0.75) = 0.3 V

Reduction potential means the tendency to reduce itself, i.e SO if we need reducing agent, then we need elements having more oxidising potential or reversing reduction potential order.
The order of reduction potential - O < N < M
So the order of reducing agent = M < N < O

Since anode is negatively charged and in anode oxidation takes place, so the element having lower SRP value would act as anode. so answer is K⁺/K.