the polarity of induced emf is always such that it tends to produce a current which opposes the change in magnetic flux that produced it
lenz law is xplained by using law of conservation of energy
if induced current in coil is due to increase in flux then directio of induced flux is so oriented as to decrease the external flux and vice versa.the energy needed to do work is converted into electrical energy to establish current in circuit
Approve if usefull