There is no earthing pin, only a socket with a metallic rim. Will it require some special socket that has a projecting earth pin? This is for use in India @ 230W. My adaptor is 85w.
The ground / earth is comprised of the outer-most two pins in the MagSafe connector (both original and the thinner + wider MagSafe 2) and requires that the ground be connected to the other end of your AC to DC adapter.
Rather than using a two prong plug, you could use a longer two prong cord and then ground the metal disc that serves to hold the "duck head" on the transformer/rectrifier/filter that makes up the bulk of the MagSafe adapter.
The transformer is double insulated and thus does not require to be grounded. It's the same with your mobile charger and external hard-drive PSU.
The outer most pins are ground (-), the 2nd and 4th are high (+) and the middle is for the Mac to signal the led on the connector:
The ground in the connector is NOT the same as the ground in your wall. The connector uses DC and the wall AC, and therefore it sounds complicated.
The MagSafe Power cable can either put an extension cable or a plug on the 'brick'. I've noticed that if I only use the plug on the brick, then the aluminium case 'tingles' when I touch it.
If I use the extension cable on the brick, then the tingling is not present. The Apple plugs don't connect to the earth pin, but the extension cables do. See this answer.