Answer : The number of ice cubes melt must be, 13
Explanation :
First we have to calculate the mass of water.

Density of water = 1.00 g/mL
Volume of water = 650 mL

Now we have to calculate the heat released on cooling.
Heat released on cooling = 
where,
m = mass of water = 650 g
c = specific heat capacity of water = 
= final temperature = 
= initial temperature = 
Now put all the given values in the above expression, we get:
Heat released on cooling = 
Heat released on cooling = 78793 J = 78.793 kJ (1 J = 0.001 kJ)
As, 1 ice cube contains 1 mole of water.
The heat required for 1 ice cube to melt = 6.02 kJ
Now we have to calculate the number of ice cubes melted.
Number of ice cubes melted = 
Number of ice cubes melted = 
Number of ice cubes melted = 13.1 ≈ 13
Therefore, the number of ice cubes melt must be, 13