[Rutherford]

Which metal is best to use as a protection of steel from corrosion
Ca,Zn,Cu,Hg,Ag? I know that Ca and Zn are before Fe. The answer is Zn, but I don't know why Ca isn't better for protection because Ca has better reducing ability than Zn.

[Borek]

Have you ever seen piece of Zn in water? Piece of Ca in water?

[Arkcon]

Yes, this is a typical 'A-ha Gotcha' they give new students in beginners chemistry.  Good work so far, you are correct that both Zn and Ca are symbols on the table, more reactive than Fe.  Now, for the part that makes you a smart person, and not a table reader -- and my statement has a hint:  

You want to protect an Ironboat from the effects of salt Water corrosion, what do you plate it with, Zinc metal, or Calcium metal?

Nobody give this one away.  Lots of people want to dump answers -- presumably for 'I'm a helper' brownie points.  This question requires logical thinking.  Raderford: needs to solve this one.  At the risk of sounding conceited, when I was a kid in high school, I solved this one, myself, in seconds.  Be on the lookout for more tricks like this.

[Rutherford]

Ca reacts faster with water so it is spent faster?

[Arkcon]

Good.  But even more so ... you can buy zinc coated roofing nails called galvanized nails at the hardware store, the zinc coating protects the iron nail from rusting for years.  Go to the hardware store and buy a lump of calcium or sodium metal, tell them you really want to protect some iron from corrosion.  Ask them where they keep the jar of sodium and calcium lumps, and pick me up a handful while you're there.

[Rutherford]

I will . Thanks for the help.

[Arkcon]

What's that *sizzle* noise I hear?

[Rutherford]

Sizzle means?

[Borek]

http://en.wiktionary.org/wiki/sizzle

[mrshaikh1960]

with regard your question this is called sacrifice corrosion in which we use that metal which corroded instead of that one to whom u want be safe