Answer : The molal freezing point depression constant of liquid X is, 
Explanation : Given,
Mass of urea (solute) = 5.90 g
Mass of liquid X (solvent) = 450 g = 0.450 kg
Molar mass of urea = 60 g/mole
Formula used :

where,
= change in freezing point
= freezing point of solution = 
= freezing point of liquid X = 
i = Van't Hoff factor = 1 (for non-electrolyte)
= Molal-freezing-point-depression constant = ?
m = molality
Now put all the given values in this formula, we get


Therefore, the molal freezing point depression constant of liquid X is, 
Explanation:
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The iupac name of the compound will be hex-3-yne or 3-hexyne. By marking number of carbon in the given compound, it was found that triple bond comes at third position and there are total 6 carbon in the compound. So it will have Hex as a prefix and as it contains triple bond so it will have yne as a suffix and as the triple bond is at third position, so it will be hex-3-yne or 3-hexyne.