Theory:

When metals react with water, metal oxide and hydrogen gas are produced. When soluble metal oxides dissolve in water, metal hydroxide is produced. On the other hand, not all metals react with water.
 
Metal+WaterMetaloxide+HydrogenMetaloxide+WaterMetalhydroxide
 
Metals like potassium and sodium react aggressively with cold water. In the case of sodium and potassium, the reaction is so violent and exothermic that the released hydrogen catches fire immediately.
 
2Ks+2H2Ol2KOHaq+H2g+Heatenergy2Nas+2H2Ol2NaOHaq+H2g+Heatenergy
 
Calcium reacts with water less aggressively. The heat released is insufficient for the hydrogen to catch fire.
 
Cas+2H2OlCaOH2aq+H2g
 
Calcium begins to float because the hydrogen gas bubbles that develop adhere to the metal's surface. Magnesium is unaffected by cold water. It forms magnesium hydroxide and hydrogen when it combines with hot water. It also starts floating due to the bubbles of hydrogen gas sticking to its surface.

Aluminium, iron and zinc do not react with either cold or hot water. However, when they come into contact with steam, they produce metal oxide and hydrogen.
 
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Metals like aluminium, iron and zinc contact with steam, forming metal oxide and hydrogen.
 
Lead, copper, silver and gold do not react with water at all.
 
2Als+3H2OgAl2O3s+3H2g3Fes+4H2OgFe3O4s+4H2g
 
Key points:
  
Metals
Reaction with normal water
Reaction with cold water
Reaction with hot water
Reaction with steam
Catches fire
Floats on water
\(Na\), \(K\)
 
 __
Yes
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__
Yes
__
\(Ca\)
 
Yes
__
__
__
__
Yes
\(Mg\)
 
__
__
Yes
__
__
__
\(Al\), \(Fe\), \(Zn\)
__
__
__
Yes
__
__
\(Pb\), \(Cu\), \(Ag\), \(Au\)
__
__
__
__
__
__
 
Their increasing order of reactivity with cold water:

\(Ca < K < Na\)
 
Their decreasing order of reactivity with water:

\(Na > K > Ca > Mg > Al > Fe > Pb > Cu > Ag > Hg\)