Step 1: Understanding the Concept:
Interhalogen compounds are unique chemical species formed through the direct or indirect reaction between two different halogen elements. These compounds are binary in nature and generally follow the formula \(XY_{n}\), where \(X\) represents the less electronegative (larger) halogen and \(Y\) represents the more electronegative (smaller) halogen. The physical state of these molecules at a specific temperature, such as 25$^{\circ}$C (standard room temperature), is primarily dictated by the strength of their intermolecular forces. In non-polar or weakly polar covalent molecules like interhalogens, the dominant intermolecular forces are Van der Waals forces, specifically London dispersion forces and dipole-dipole interactions.
The strength of these forces is heavily dependent on the total number of electrons and the surface area of the molecule. Larger atoms with higher atomic numbers have more electrons and a more polarizable electron cloud, leading to stronger instantaneous dipoles. Consequently, as the molecular mass and size of the central halogen atom increase, the boiling point of the compound rises, causing a transition from the gaseous phase to the liquid or solid phase.
Step 2: Detailed Explanation:
To accurately identify the non-gaseous compound, we must evaluate the physical properties and molecular characteristics of each option provided:
(1) ClF (Chlorine monofluoride): This is the simplest type of interhalogen molecule. It is a diatomic molecule composed of one Chlorine and one Fluorine atom. Because both atoms are relatively small and located in the upper part of the periodic table, the total molecular weight is low (approximately 54.45 g/mol). The intermolecular forces are very weak, resulting in an extremely low boiling point of approximately -100.1$^{\circ}$C. Since 25$^{\circ}$C is significantly higher than its boiling point, ClF exists as a colorless gas.
(2) BrF\(_{3}\) (Bromine trifluoride): This molecule consists of a central Bromine atom surrounded by three Fluorine atoms. Bromine belongs to the 4th period and is much larger and heavier than Chlorine. The molecule adopts a T-shaped geometry due to the presence of two lone pairs on the central Bromine atom. This asymmetry creates a significant permanent dipole moment. The combination of a higher molecular mass (136.9 g/mol) and strong dipole-dipole attractions raises its boiling point to 125.7$^{\circ}$C. Since the boiling point is well above room temperature, BrF\(_{3}\) exists as a straw-colored, dense liquid.
(3) IF\(_{3}\) (Iodine trifluoride): While Iodine is the heaviest of the common halogens, IF\(_{3}\) is notorious for its instability. It is generally synthesized at very low temperatures and tends to decompose or disproportionate rapidly into IF and IF\(_{5}\) at room temperature. In most standard academic classifications for stable interhalogens at STP, it is not listed as a primary liquid; rather, it is often discussed as a transient gaseous or solid species under specific controlled conditions.
(4) ClF\(_{3}\) (Chlorine trifluoride): This is a highly reactive and volatile compound. Although it has a T-shaped geometry like BrF\(_{3}\), the central atom is Chlorine, which is smaller. Its boiling point is approximately 11.7$^{\circ}$C. At the specified temperature of 25$^{\circ}$C, ClF\(_{3}\) has already surpassed its boiling point and exists as a colorless gas.
Step 3: Final Answer:
By analyzing the boiling points and intermolecular attractions, it is clear that Bromine trifluoride (BrF\(_{3}\)) is the only stable compound among the choices that remains in the liquid state at 25$^{\circ}$C. The others either exist as gases or are unstable.
Therefore, the compound not in the gaseous phase is BrF\(_{3}\).
Hence, the correct answer is option (2).