Valency of aluminium is:

Options

A. 2
B. 3
C. 4
D. 5

Explanation

To determine the valency of aluminum, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Valency**:
- Valency is defined as the combining capacity of an element. It indicates how many electrons an atom can lose, gain, or share when it forms a chemical bond.

**Hint**: Remember that valency relates to how elements interact with each other to form compounds.

2. **Identify the Atomic Number of Aluminum**:
- Aluminum has an atomic number of 13. This means it has 13 protons and, in a neutral atom, also 13 electrons.

**Hint**: The atomic number tells you the number of protons and electrons in a neutral atom.

3. **Determine the Electron Configuration**:
- The electron configuration of aluminum can be written as:
- 1s² 2s² 2p⁶ 3s² 3p¹
- This shows that aluminum has 3 electrons in its outermost shell (the third shell).

**Hint**: The outermost shell (valence shell) is crucial for determining how an element will bond.

4. **Understanding the Octet Rule**:
- The octet rule states that atoms tend to gain, lose, or share electrons to achieve a full outer shell of 8 electrons.
- Aluminum has 3 electrons in its outer shell and needs to lose these 3 electrons to achieve a stable configuration of 2, 8 (which corresponds to the electron configuration of neon).

**Hint**: The octet rule helps explain why elements behave the way they do in bonding.

5. **Determine the Valency of Aluminum**:
- Since aluminum can lose 3 electrons to achieve a stable electron configuration, its valency is 3.
- This means aluminum typically forms +3 ions (Al³⁺) when it reacts with other elements.

**Hint**: The valency can be positive if electrons are lost, negative if gained, or can vary if electrons are shared.

### Final Answer:
The valency of aluminum is **3**.