The alkali metals:

Options

A. form salt like ionic hybrides
B. posses low ionisation potential
C. have high affinity for non-metals
D. have low density

Answer

To solve the question regarding the properties of alkali metals, we will evaluate each statement one by one and determine their correctness based on the known characteristics of alkali metals.

### Step-by-Step Solution:

1. **Identify Alkali Metals**:
- Alkali metals include Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), and Cesium (Cs).
- They are located in Group 1 of the periodic table.

**Hint**: Remember the group number of alkali metals and their common properties.

2. **Evaluate Statement A**:
- The statement claims that alkali metals may form salt-like ionic hydrides.
- Alkali metals react with hydrogen to form ionic hydrides (e.g., NaH, LiH).
- This statement is **correct**.

**Hint**: Think about how alkali metals interact with hydrogen and the type of compounds they form.

3. **Evaluate Statement B**:
- The statement claims that alkali metals possess low ionization potential.
- Alkali metals have a single electron in their outermost shell (ns¹), which they can easily lose, resulting in low ionization energy.
- This statement is **correct**.

**Hint**: Consider the electronic configuration of alkali metals and how it relates to their reactivity.

4. **Evaluate Statement C**:
- The statement claims that alkali metals have a high affinity for non-metals.
- Alkali metals tend to lose their outer electron and readily react with non-metals (e.g., halogens) to form ionic compounds.
- This statement is **correct**.

**Hint**: Reflect on the nature of ionic bonds and how metals and non-metals interact.

5. **Evaluate Statement D**:
- The statement claims that alkali metals may have low density.
- Alkali metals are indeed known for their low density; for example, lithium, sodium, and potassium are less dense than water.
- This statement is **correct**.

**Hint**: Consider the physical properties of alkali metals and how they compare to other metals.

### Conclusion:
- All four statements (A, B, C, and D) regarding alkali metals are correct.

**Final Answer**: All statements about alkali metals (A, B, C, and D) are correct.