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The most convenient method to protect the bottom of ship made of iron is : -
A
Coating it with red lead oxide
B
White tin plating
C
Connecting it with Mg block
D
Connecting it with Pb block
Detailed Solution
The hull of a ship is always in contact with sea water, so paints and coatings wear off.
In cathodic protection (sacrificial anode method), a more active metal such as magnesium or zinc is connected to the iron. Magnesium ($E^\circ = -2.37$ V) is more easily oxidised than iron ($E^\circ = -0.44$ V), so it corrodes instead of iron, and the iron acts as the cathode.
The magnesium blocks are replaced from time to time.
Lead is less active than iron, so connecting lead would make iron corrode faster; a tin coating protects only while unbroken.
So the most convenient method is connecting it with a Mg block.
In cathodic protection (sacrificial anode method), a more active metal such as magnesium or zinc is connected to the iron. Magnesium ($E^\circ = -2.37$ V) is more easily oxidised than iron ($E^\circ = -0.44$ V), so it corrodes instead of iron, and the iron acts as the cathode.
The magnesium blocks are replaced from time to time.
Lead is less active than iron, so connecting lead would make iron corrode faster; a tin coating protects only while unbroken.
So the most convenient method is connecting it with a Mg block.