Number of unpaired electrons in Cr =6 (b) Iron (Z=26) EC=[Ar]3d64s2
Number of unpaired electrons =4 (c) Manganese (Z=25) EC=[Ar]3d54s2
Number of unpaired electrons =5 We know that a pn-junction diode is operated in forward bias only. ∴ For positive half cycle, the circuit will look like,