Mark the correct statements out of the following:

Options

A. He and the highest `I.E_(1)` in the periodic table
B. Cl has the highest E.A. out of all the elements in the periodic table
C. Hg and Br are liquid at room temperature
D. In anyperiod, the atomic radius of the noble gas is lowest

Explanation

To solve the question, we need to analyze each statement provided and determine if they are correct or incorrect based on our knowledge of periodic properties.

### Step-by-Step Solution:

1. **Statement 1: Helium has the highest ionization enthalpy in the periodic table.**
- **Analysis:** Ionization enthalpy is the energy required to remove an electron from an atom. Helium, being a noble gas with a complete outer shell, has a very high ionization energy due to its small atomic size and strong effective nuclear charge. Therefore, this statement is **true**.

2. **Statement 2: Chlorine has the highest electron affinity out of all the elements in the periodic table.**
- **Analysis:** Electron affinity is the energy change when an electron is added to a neutral atom. Chlorine does indeed have a higher electron affinity than fluorine, despite fluorine being smaller. The reason is that the added electron in fluorine experiences significant repulsion from the other electrons, which reduces its electron affinity. Thus, this statement is also **true**.

3. **Statement 3: Mercury and bromine are liquid at room temperature.**
- **Analysis:** Mercury (Hg) is a liquid at room temperature, and bromine (Br) is also a liquid at room temperature. Therefore, this statement is **true**.

4. **Statement 4: The atomic radius of noble gases is lowest.**
- **Analysis:** This statement is incorrect. Noble gases actually have the largest atomic radii compared to other elements in the same period due to their full valence shells and weak interatomic forces. Therefore, this statement is **false**.

### Conclusion:
The correct statements are:
- Statement 1: True
- Statement 2: True
- Statement 3: True
- Statement 4: False

Thus, the correct answers are statements 1, 2, and 3.

### Final Answer:
The correct statements are: 1, 2, and 3.

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