Which of the following elements is usually a liquid at room temperature?

• A. Bromine (Br)
• B. Chlorine (Cl)
• C. Sodium (Na)
• D. Mercury (Hg)

Answer: (D)

Verified step by step guidance

1. Understand the question: It asks which element is usually a liquid at room temperature (around 25°C). This means we need to identify the element with a melting point below or near room temperature but a boiling point above it.
2. Recall the physical states of the given elements at room temperature: Bromine (Br) is a reddish-brown liquid, Chlorine (Cl) is a greenish gas, Sodium (Na) is a solid metal, and Mercury (Hg) is a silvery liquid metal.
3. Review the melting and boiling points of these elements: For example, Mercury (Hg) melts at approximately -39°C and boils at 357°C, which means it is liquid at room temperature.
4. Compare the melting points to room temperature: Elements with melting points below 25°C and boiling points above 25°C will be liquid at room temperature.
5. Conclude that Mercury (Hg) is the element that is usually liquid at room temperature, unlike Bromine, Chlorine, or Sodium.