Answer:
Explanation:
Depression in freezing point is given by:

= Depression in freezing point
i= vant hoff factor = 1 (for non electrolyte like urea)
= freezing point constant = 
m= molality

Weight of solvent (X)= 950 g = 0.95 kg
Molar mass of non electrolyte (urea) = 60.06 g/mol
Mass of non electrolyte (urea) added = ?


Thus
urea was dissolved.
Given is the specific heat of water equal to 4.18 Joule per gram per *C.
This means to raise the temperature of 1 g of water by 1 degree Celsius we need 4.18 joule of energy.
Now, look at the question. We are asked that how much amount of energy would be required to raise the temperature of 25 g of water by (54-50) = 4 degree celsius.
To do so we have formula
Q = m C (temperature difference)
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