Question

write balanced equations for the reaction of Sodium Potassium and calcium in cold water

Answer 1

Hey mate..

2Na+2H2O-2NaOH+H2
2K+2H2O-2KOH+H2
2Ca+2H2O-Ca(OH)2+H2

HOPE IT HELPS...☺

Answer 2

All of these metals react vigorously or even explosively with cold water. In each case, a solution of the metal hydroxide is produced together with hydrogen gas. 
 
 2X (s) + 2H2O (l) → 2XOH (aq) + H2 (g) 
 
 This equation applies to any of these metals and water - just replace the X by the symbol you want. 
 
 For your your reaction, the following would occur (written form and balanced equation): 
 
 Potassium + Water → Potassium Hydroxide + Hydrogen 
 
 2K + 2H2O → 2KOH + H2