about corrosion-resistance!!

Copper (Cu) is more resistant to corrsion than nickel (Ni).

This is because copper is less reactive than nickel.

Reactivity: Fe > Ni > Sn > Pb > Cu

Nickel is more reative than copper , this can be shown easily from using US coins--a penny & dime . A penny is made of pure copper which is oxidised to CuO becoming dull in color . Just immerse it in vinegar then it turns back to shining. CuO + 2CH3COOH------> (CH3COO)2Cu +H2O As the copper acetate is soluble in water so the coin exposes its bright copper surface .

As dime is plated with nickel when it is immersed in the above copper acetate solution .(CH3COO)2Cu + Ni------> Cu + (CH3COO)2Ni Since copper is more reactive , Cu is replaced . As the dime is copper plated outside with nickel so it becomes copper in color .