Enthalpy

The standard enthalpy change of fusion ( ) refers to the heat absorbed when one mole of a substance undergoes fusion (melts) at constant pressure.
- H O: Water has a relatively moderate , as its intermolecular hydrogen bonding makes it require a significant amount of heat to melt, but it is not the highest among the options listed.
- CO: Carbon monoxide has a low , as its molecular forces are relatively weak, requiring less energy to melt. - C H : Benzene (C₆H₆) has a higher than CO but is still lower than that of ionic compounds.
- CCl : Carbon tetrachloride has a moderate , though not as high as ionic compounds.
- NaCl: Sodium chloride is an ionic compound, and ionic bonds are very strong. Therefore, NaCl requires a large amount of energy to overcome the lattice energy during fusion, resulting in a higher enthalpy change of fusion compared to the other molecules listed.
Thus, the correct answer is (E) NaCl.

Extensive properties are those that depend on the amount or size of the substance present in the system. They are proportional to the quantity of material. - Density is an intensive property because it does not depend on the amount of substance. It is a ratio of mass to volume. - Volume is an extensive property because it is directly proportional to the amount of substance present. The more substance you have, the greater the volume. - Heat capacity is also an extensive property because it depends on the quantity of material. A larger amount of material will absorb more heat for a given temperature change. Thus, Volume is the correct answer as an extensive property.

The bond enthalpy refers to the energy required to break one mole of bonds in a molecule in its gaseous phase. The strength of a bond is influenced by factors such as bond length and the electronegativity difference between the atoms involved.

1. Step 1: Compare the types of bonds. - A double bond (like and ) is stronger than a single bond but weaker than a triple bond (like ). - A triple bond is the strongest and thus has the highest bond enthalpy.

2. Step 2: Analyze each bond. - The C = C bond is weaker compared to the C = O and C \equiv N bonds because oxygen and nitrogen are more electronegative than carbon, making their bonds stronger. - The C = O bond is stronger than C = C because oxygen is more electronegative. - The C \equiv N bond is stronger than C = O and C = C due to the triple bond. Thus, the least bond enthalpy is found for the C = C bond.