Let's analyze each statement:

This statement is true. Molecular crystals are formed by discrete molecules held together by weak intermolecular forces, primarily van der Waals forces (London dispersion forces, dipole-dipole interactions) and sometimes hydrogen bonding. Examples include solid CO\u2082, iodine, and sugar.

This statement is true. For isomeric organic compounds, increased branching leads to a more spherical shape, reducing the surface area available for intermolecular contact. This decreases the strength of London dispersion forces (a type of van der Waals force), resulting in lower boiling points. For example, n-pentane has a higher boiling point than neopentane.

This statement is true. Graphite consists of layers of carbon atoms arranged in hexagonal rings. Within each layer, carbon atoms are covalently bonded. However, the layers themselves are held together by weak van der Waals forces, which allows them to slide past each other, giving graphite its lubricating properties.

This statement is false. Let's compare the boiling points of hydrides of Group 15 elements. For Group 15 hydrides (NH\u2083, PH\u2083, AsH\u2083, SbH\u2083, BiH\u2083), the boiling point generally increases down the group due to increasing molecular size and stronger London dispersion forces. However, NH\u2083 has an exceptionally high boiling point due to strong intermolecular hydrogen bonding. The boiling point order is generally: PH\u2083 < AsH\u2083 < NH\u2083 < SbH\u2083 < BiH\u2083. Therefore, the boiling point of ${\mathrm{SbH}}_3$ is greater than that of ${\mathrm{NH}}_3$.

Correct Answer: (D)