Question

The compound with the lowest boiling point among the following is:
(A) HF
(B) HCl
(C) HI
(D) HBr

Answer 1

Hint : To answer this question, we first need to understand what are compounds. A chemical compound is a substance made up of numerous identical molecules bound together by chemical bonds and made up of atoms from different elements. As a result, a molecule made up of only one element's atoms is not a compound.

Complete Step By Step Answer:
Boiling point – The temperature at which the pressure exerted by the surroundings on a liquid is equaled by the pressure exerted by the liquid's vapor; at this temperature, adding heat causes the liquid to change into its vapor without raising the temperature.
HF – HF stands for hydrogen fluoride, which is a chemical compound with the formula HF. The main industrial source of fluorine is this colorless gas or liquid, which is usually in the form of an aqueous solution called hydrofluoric acid. It is used to make a variety of essential substances, such as medicines and polymers, such as polytetrafluoroethylene (PTFE). Boiling point of this compound is 292.5 Kelvin.
HCl – Hydrochloric acid, commonly known as muriatic acid, is a hydrogen chloride aqueous solution. It's a colorless liquid with a strong, pungent odor. It's considered a strong acid. Most animal species' digestive systems, including humans', contain it as a component of gastric acid. Boiling point of this compound is 188 Kelvin.
HI – Hydrogen iodide (HI) is a hydrogen halide and a diatomic molecule. Hydroiodic acid, or hydriodic acid, is a powerful acid made up of aqueous solutions of HI. The difference between hydrogen iodide and hydroiodic acid is that the former is a gas under normal conditions, whilst the latter is an aqueous solution of the gas. The boiling point of this compound is 237.8 Kelvin.
HBr – The diatomic molecule hydrogen bromide (HBr) is dissolved in water to produce hydrobromic acid, a powerful acid. The aqueous solution of "constant boiling" hydrobromic acid distils at 124.3 °C and contains 47.6% HBr by mass, making it a stronger acid than hydrochloric acid but not as strong as hydroiodic acid. One of the most powerful mineral acids is hydrobromic acid. Boiling point of this compound is 395 Kelvin.
So, we conclude that HBr has the highest boiling point.

Note :
The boiling point of a compound is affected by the relative intensity of intermolecular forces such as ionic, hydrogen bonding, dipole-dipole interaction, and Vander Waals dispersion force. The impact of these forces is determined by the functional group that is present.