Answer:
I and II.
Explanation:
The interactions between the molecules in a substance are associated with the type of the substance. For ionic compounds, the atoms are joined together by the ion-ion interactions, for metallic compounds, by metallic interactions, and, for molecular compounds, they can be attracted by London forces, dipole-dipole forces or by hydrogen bonds.
The London forces exist in nonpolar molecules, which are the ones formed by nonpolar bonds (elements with the same electronegativity), or form bonds with the same polarity that is opposite, and so are canceled. The dipole-dipole force exists in polar molecules, and so, the atoms have partial charges, and the interactions are stronger than in London forces. If the dipole-dipole exists with hydrogen and a high electronegative element (N, O, or F), the bond is even strong and is called a hydrogen bond.
So, let's analyze the statements:
I. As said above, dipole-dipole occurs in polar molecules, so they may have polar bonds, and the statement is correct;
II. Because the polarity of the bonds is a vector when the shape is symmetric, is more likely to the polarities be canceled, so it's usual to the polar molecules be asymmetric, and the statement is correct;
III. Because the dipole-dipole is a strong force, it's difficult to break it and the substance needs more energy to change phase, so they have a high boiling point, and the statement is incorrect;
IV. Because the shape of the molecule is asymmetric, the surface area intends to be small, the atoms are distributed in a small place. If the molecule is linear, for example, then the atoms are distributed in large spaces, so the statement is incorrect.
