a. Oxides and peroxides of alkali metals are diamanetic and colourless.
b. Superoxides of the alkali metals are paramagnetic.
c. Li is the least electronegative alkali metal.
d. Potassiumis the most abundant alkail metal in the erth's crust.
e. `LiCI_(2)` and `MgCI_(2)` are deliquesent.
f. Lithium reacts with nitrogen to form nitride.

Explanation

To analyze the statements provided about alkali metals, we will evaluate each statement one by one and determine their validity.

### Step 1: Evaluate the first statement
**Statement a:** Oxides and peroxides of alkali metals are diamagnetic and colorless.

- **Analysis:** Alkali metals form oxides (e.g., Na2O) and peroxides (e.g., Na2O2). Both of these compounds do not have unpaired electrons, which means they are diamagnetic. Additionally, they are typically colorless in their pure forms.
- **Conclusion:** This statement is **true**.

### Step 2: Evaluate the second statement
**Statement b:** Superoxides of the alkali metals are paramagnetic.

- **Analysis:** Superoxides (e.g., KO2) contain the superoxide ion (O2^-), which has unpaired electrons, making them paramagnetic.
- **Conclusion:** This statement is **true**.

### Step 3: Evaluate the third statement
**Statement c:** Li is the least electronegative alkali metal.

- **Analysis:** Electronegativity increases as we move down the group in the periodic table. Lithium (Li) is indeed the least electronegative alkali metal, with a value of about 1.0 on the Pauling scale.
- **Conclusion:** This statement is **true**.

### Step 4: Evaluate the fourth statement
**Statement d:** Potassium is the most abundant alkali metal in the Earth's crust.

- **Analysis:** While potassium (K) is abundant, sodium (Na) is actually the most abundant alkali metal in the Earth's crust. Therefore, this statement is incorrect.
- **Conclusion:** This statement is **false**.

### Step 5: Evaluate the fifth statement
**Statement e:** LiCl2 and MgCl2 are deliquescent.

- **Analysis:** Deliquescent substances absorb moisture from the air and dissolve in it. Lithium chloride (LiCl) is deliquescent, but magnesium chloride (MgCl2) is also known to be deliquescent. However, the notation "LiCl2" is incorrect; it should be LiCl. Therefore, the statement is misleading due to the incorrect formula.
- **Conclusion:** This statement is **false**.

### Step 6: Evaluate the sixth statement
**Statement f:** Lithium reacts with nitrogen to form nitride.

- **Analysis:** Lithium does react with nitrogen to form lithium nitride (Li3N). This is a well-known reaction.
- **Conclusion:** This statement is **true**.

### Summary of the Evaluation:
- a. True
- b. True
- c. True
- d. False
- e. False (due to incorrect formula)
- f. True