The element which exists in the liquid state at `30^(@)C`.

Options

A. bromine
B. mercury
C. gallium
D. all of these

Explanation

To determine which elements exist in the liquid state at 30°C, we can analyze the properties of the elements mentioned. Here’s a step-by-step solution:

### Step 1: Identify the Elements
The elements we need to consider are:
- Bromine (Br)
- Mercury (Hg)
- Gallium (Ga)

### Step 2: Check the State of Each Element at 30°C
1. **Bromine (Br)**:
- Bromine is a halogen and is known to be a liquid at room temperature (approximately 20°C). Therefore, it will definitely be in the liquid state at 30°C.

2. **Mercury (Hg)**:
- Mercury is a metal that is also liquid at room temperature (approximately -39°C). Thus, it will remain in the liquid state at 30°C.

3. **Gallium (Ga)**:
- Gallium is a metal that has a melting point of about 29.76°C. At 30°C, gallium will melt and be in the liquid state.

### Step 3: Conclusion
All three elements: Bromine, Mercury, and Gallium exist in the liquid state at 30°C.

### Final Answer
The elements that exist in the liquid state at 30°C are:
- Bromine (Br)
- Mercury (Hg)
- Gallium (Ga)