Problem 92 - A Complete Resource Book in Chemistry for JEE Main

Question

The elements which exist in the liquid state at room temperature are 1\. Na 2\. Br 3\. \(\mathrm{Hg}\) 4\. Ga (a) \(1,2,3\) (b) 2,3 (c) 2,4 (d) \(1,2,3\)

Step-by-Step Solution

Answer

Option (b) 2,3 (Br, Hg) are liquids at room temperature.

Step 1: Determine Room Temperature Conditions

Room temperature typically refers to a temperature of around 20°C to 25°C (68°F to 77°F). Elements that are liquid at this temperature are quite rare. They must have melting points below or near this range.

Step 2: Analyze Each Element

Now, let's look at each listed element: 1. Na (Sodium) has a melting point of 97.8°C, so it is solid at room temperature. 2. Br (Bromine) has a melting point of -7.2°C, so it is liquid at room temperature. 3. Hg (Mercury) has a melting point of -38.83°C, so it is liquid at room temperature. 4. Ga (Gallium) has a melting point of 29.76°C, which means it is solid just below room temperature but can melt in the hand, often considered solid at room temperature.

Step 3: Identify Liquid Elements

From Step 2, identify which elements are liquid at room temperature. Bromine (Br) and Mercury (Hg) both have melting points below room temperature, making them liquids.

Step 4: Choose the Correct Answer

Look at the options provided. Option (b) includes elements 2,3 (Br, Hg), which are liquid at room temperature. Thus, the correct answer is option (b).

Key Concepts

Melting Point

The melting point of a substance is the temperature at which it changes from a solid to a liquid. For elements, this temperature can vary greatly across the periodic table. An element's melting point determines the physical state it will most commonly exist in at a given temperature.
Elements with higher melting points are typically solids at room temperature, while those with lower melting points might be liquids.
Understanding an element's melting point gives insight into its behavior in different conditions and is crucial for applications that require precise temperature control.

• High melting point - solid at room temperature
• Low melting point - can be liquid at room temperature

For example, Sodium (Na) has a melting point of 97.8°C, making it a solid at room temperature. In contrast, Bromine (Br) with a melting point of -7.2°C and Mercury (Hg) with a melting point of -38.83°C are liquids at room temperature.

Liquid Elements

Liquid elements are quite rare at room temperature. Most elements are either gases or solids under these conditions. A liquid element will have a melting point that falls below typical room temperature values of 20°C to 25°C (68°F to 77°F). This means that they have low melting points that allow them to remain in a liquid state instead of solidifying.

• Bromine (Br) and Mercury (Hg) are the most commonly acknowledged liquid elements at room temperature.
• Gallium (Ga), though solid at just below room temperature, can melt on contact with a warm hand.

These elements' unique physical states make them intriguing for both study and practical applications. Mercury, for instance, is famous for its use in thermometers because it remains liquid even at temperatures well below room temperature.

Room Temperature

Room temperature is a term used to describe a range of temperatures that are comfortable for humans in indoor settings, typically around 20°C to 25°C (68°F to 77°F). This range can vary slightly based on local climate and personal comfort, but it serves as a general baseline for many scientific and practical purposes. Elements that are liquid at room temperature are those with a melting point below this range.
Understanding the concept of room temperature is important in chemistry and physics, as it is a common reference point for experiments and the behavior of elements.

• Prescribes necessary conditions for living spaces and materials usage.
• Influences the state of matter of elements and compounds commonly encountered daily.

In summary, only a few elements, like Bromine and Mercury, naturally exist as liquids at room temperature, making them exceptions to the norm of solid nongaseous elements under these conditions.