help me with this really confusing chemistry o level mcq ?

[Iishrak]

It came in june 2005 paper 1
Question 28- Which metal reacts quickly with cold water only when it is finely powdered? A- Calcium B- Copper C- Sodium D- Magnesium. I chose C as sodium is the most reactive out of all of them (according to the reactivity series) but the answer is D?

in examiner's report : This was answered correctly by only a third of the candidates. In essence the question was testing
understanding of the reactivity series and it is surprising that two fifths of the lower-scoring candidates chose
sodium!

, and i have googled a lot about it and it seems like magnesium to react with cold water is slowly
source : http://www.gcsescience.com/pt17.htm, confused :S help

 

[Mirha Ayesha]

Sodium is very reactive and it can react with cold water even when not in a powdery state. This goes for calcium as well. Magnesium, however, is lower down reactivity series and need to be in powder form to react with cold water. Copper does not react with water or acids

 

[Iishrak]

Sodium is very reactive and it can react with cold water even when not in a powdery state. This goes for calcium as well. Magnesium, however, is lower down reactivity series and need to be in powder form to react with cold water. Copper does not react with water or acids

how does that explain the answer is magnesium -_-
and that link says magnesium doesn't react with cold water , or slow reaction -_-

 

[nidz]

Magnesium does react but slowly. In powdered form, the surface area increases so it would be able to react. That link says
"Even finely powdered magnesium reacts only very slowly."

 

[ahmad802]

ok the thing is that reaction between Sodium and Cold Water Occurs but it is so violent that it may prove fatal therefore such reactions are avoided. Same is the Case with Calcium. Copper being low in the reactivity series donot react with cold water. Magnesium comes somewhere between Sodium/Calcium and Copper therefore it is the best choice. Yeah one thing more is also very helpful. The following is an easy way to learn reactivity series
Learn this line
Please = Pottasium
send = Sodium
Cats = Calcium
Monkeys = Magnesium
And = Aluminium
Cute = Carbon
Zebras = Zinc
in = Iron
Large = Lead
Hired = Hydrogen
Cages = Copper
Make = Mercury
Sure = Silver
Patlocked = Platinum
HOPE THIS HELPS
Any other question feel free to ask @ [email protected]

 

[Iishrak]

ok the thing is that reaction between Sodium and Cold Water Occurs but it is so violent that it may prove fatal therefore such reactions are avoided. Same is the Case with Calcium. Copper being low in the reactivity series donot react with cold water. Magnesium comes somewhere between Sodium/Calcium and Copper therefore it is the best choice. Yeah one thing more is also very helpful. The following is an easy way to learn reactivity series
Learn this line
Please = Pottasium
send = Sodium
Cats = Calcium
Monkeys = Magnesium
And = Aluminium
Cute = Carbon
Zebras = Zinc
in = Iron
Large = Lead
Hired = Hydrogen
Cages = Copper
Make = Mercury
Sure = Silver
Patlocked = Platinum
HOPE THIS HELPS
Any other question feel free to ask @ [email protected]

Thanks for that but i got another one to remember the reatcivity series about the answer so from now on we also have to think reaction in terms of safety O.O

 

[Iishrak]

Magnesium does react but slowly. In powdered form, the surface area increases so it would be able to react. That link says
"Even finely powdered magnesium reacts only very slowly."

And the question says reacts very quickly.

 

[nidz]

And the question says reacts very quickly.

I guess according to CIE, it would react quickly.

 

[Faizan Muhammmad]

well there is a difference between reacting quickly and exploding
sodium will also react in lump form but Mg will be too slow