i would like to know about the resonance theory of indicators in detailplease help me.

In electrolysis, the cathode product is often a metal. If the cathode is completely immersed in the electrolyte, then the cathode becomes completely covered by metal. This is the basis of the technique of electroplating. In electroplating, a complete layer of a second metal is deposited on a first metal by electrolysis.

This may be done for a number of reasons. Steel bumpers on cars become more corrosion resistant when they are electroplated first with nickel and then with chromium. Steel camshafts in cars have improved wear resistance when they have been electroplated with chromium. Plain steel or aluminium parts in light fittings become more ornamental when they are electroplated with nickel and then chromium or brass.
EPNS stands for "electroplated nickel silver". Nickel silver is an alloy that contains copper, zinc, and nickel. It is often made more decorative by being covered with real silver, deposited by electrolysis.