Which of the following statements is/are true ?

Options

A. Both LiCl and `MgCl_2` are deliquescent
B. Lithium is least reactive but the strongest reducing agent amongst all the alkali metals
C. Liquid sodium metal is used as a coolant in fast breeder nuclear reactors
D. Lithium iodide is the most ionic in nature among alkali metal halides

Explanation

To determine which of the statements are true, let's analyze each statement one by one.

**Step 1: Analyze Statement A**
- **Statement A**: Both lithium chloride and magnesium chloride are deliquescent.
- **Explanation**: Deliquescent substances absorb moisture from the atmosphere. Lithium chloride (LiCl) is known to be deliquescent, as it can absorb water and form a hydrated compound (LiCl·2H2O). Magnesium chloride (MgCl2) is also deliquescent and can form MgCl2·6H2O. Therefore, this statement is **true**.

**Step 2: Analyze Statement B**
- **Statement B**: Lithium is least reactive but the strongest reducing agent amongst all the alkali metals.
- **Explanation**: Lithium has the highest ionization energy among alkali metals, making it the least reactive. However, it also has the highest standard electrode potential (E°), which means it can easily donate electrons, making it a strong reducing agent. Therefore, this statement is **true**.

**Step 3: Analyze Statement C**
- **Statement C**: Liquid sodium metal is used as a coolant in fast breeder nuclear reactions.
- **Explanation**: Liquid sodium is indeed used as a coolant in fast breeder reactors due to its excellent thermal conductivity and low melting point. It effectively absorbs heat from the nuclear reactions. Therefore, this statement is **true**.

**Step 4: Analyze Statement D**
- **Statement D**: Lithium iodide is the most ionic in nature amongst the alkali metal halides.
- **Explanation**: While lithium iodide (LiI) consists of a small lithium ion and a large iodide ion, which suggests a high ionic character, it actually has significant covalent character due to the small size of the lithium ion and the large size of the iodide ion. According to Fajan's rules, this leads to a more covalent character. Therefore, this statement is **false**.

**Conclusion:**
The true statements are A, B, and C. Thus, the correct answer is A, B, and C.