Identify the correct pair of elements among the following which are liquid at room temperature and standard pressure.
Bromine and mercury
Identifying Elements Liquid at Room Temperature
This question asks us to find the pair of chemical elements that are in a liquid state at standard room temperature and pressure.
Room temperature is generally considered to be around 20-25 degrees Celsius, and standard pressure is typically 1 atmosphere. At these conditions, most elements are solids, some are gases, and only a few are liquids.
Let's examine the state of each element mentioned in the options at room temperature and standard pressure:
- Bromine (Br): Bromine is a non-metal. It exists as a diatomic molecule, Br₂. At room temperature and standard pressure, Bromine is a volatile reddish-brown liquid.
- Fluorine (F): Fluorine is a non-metal. It exists as a diatomic molecule, F₂. At room temperature and standard pressure, Fluorine is a pale yellow gas.
- Mercury (Hg): Mercury is a metal. At room temperature and standard pressure, Mercury is a unique silvery-white liquid. It is the only metal that is liquid under these conditions.
- Rubidium (Rb): Rubidium is an alkali metal. At room temperature and standard pressure, Rubidium is a soft, silvery-white solid. Its melting point is relatively low but still above typical room temperature (around 39.3 °C).
- Thallium (Tl): Thallium is a post-transition metal. At room temperature and standard pressure, Thallium is a soft, bluish-white solid. Its melting point is well above room temperature (around 304 °C).
Now let's evaluate the given pairs based on the states of these elements:
- Bromine and fluorine: Bromine is liquid, but fluorine is a gas. This pair is incorrect.
- Mercury and rubidium: Mercury is liquid, but rubidium is a solid. This pair is incorrect.
- Bromine and thallium: Bromine is liquid, but thallium is a solid. This pair is incorrect.
- Bromine and mercury: Bromine is liquid, and mercury is liquid. This pair consists of two elements that are liquid at room temperature and standard pressure.
Therefore, the correct pair of elements that are liquid at room temperature and standard pressure is Bromine and Mercury.
| Element | Symbol | State at Room Temperature (∼25 °C) and Standard Pressure (1 atm) |
|---|---|---|
| Bromine | Br | Liquid |
| Fluorine | F | Gas |
| Mercury | Hg | Liquid |
| Rubidium | Rb | Solid |
| Thallium | Tl | Solid |
Revision Table: States of Elements
Understanding the typical state (solid, liquid, or gas) of elements at room conditions is fundamental in chemistry. Here's a quick summary:
- Most elements are solids at room temperature (metals like Iron, Gold, non-metals like Carbon, Silicon).
- Only two elements are typically liquid at room temperature and standard pressure: Bromine and Mercury.
- Eleven elements are gases at room temperature and standard pressure: Hydrogen (H₂), Nitrogen (N₂), Oxygen (O₂), Fluorine (F₂), Chlorine (Cl₂), Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn).
Additional Information: Elements Near Room Temperature
While Bromine and Mercury are the only elements liquid at standard room temperature (∼25 °C), some other elements have melting points just slightly above this temperature and can become liquid on a warm day or with slight heating:
- Gallium (Ga): Melts at 29.8 °C. It will melt if held in your hand.
- Cesium (Cs): Melts at 28.5 °C.
- Francium (Fr): Estimated melting point is around 27 °C, but it is highly radioactive and rare.
These elements highlight that the distinction between solid and liquid can be temperature-sensitive, but under standard conditions, Bromine and Mercury are the key examples of liquid elements.
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