Due to which reasons do energy losses occur in an actual transformer?

(N/A) $(i)$ Flux Leakage: Not all of the flux due to the primary coil passes through the secondary coil due to poor design of the core or air gaps in the core. It can be reduced by winding the primary and secondary coils one over the other.
$(ii)$ Resistance of the windings: The wire used for the winding has some resistance,and so energy is lost due to heat produced in the wire $(I^{2}R)$. In high current,low voltage windings,these are minimized by using thick wire.
$(iii)$ Eddy Currents: The alternating magnetic flux induces eddy currents in the iron core,causing heating. This effect is reduced by using a laminated core.
$(iv)$ Hysteresis: The magnetization of the core is repeatedly reversed by the alternating magnetic field. The resulting expenditure of energy in the core appears as heat and is kept to a minimum by using a magnetic material with low hysteresis loss.
$(v)$ Humming/Buzzing: Transformers work on $AC$ voltage; hence,in each cycle,the dimensions of the core change due to magnetostriction. As a result,the transformer produces a buzzing noise,leading to the dissipation of some electrical energy as sound.