Assertion. Coloured cations can be identified by borax bead test.
Reason. Transparent bead `(NaBO_(2) + B_(2)O_(3))` forms coloured bead with coloured cation.

Options

A. If both assertion and reason are true, and reason is the true explanation of the assertion.
B. If both assertion and reason are true, but reason not is the true explanation of the assertion.
C. If assertion is true, but reason is false.
D. If both assertion and reason are false.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- The assertion states that colored cations can be identified by the borax bead test.
- The borax bead test is a qualitative analysis method used to identify certain metal ions based on the color of the bead formed when the borax is heated with the metal cation.

**Hint:** Recall what colored cations are and how they interact with borax.

2. **Understanding the Reason:**
- The reason states that a transparent bead (composed of NaBO2 and B2O3) forms a colored bead when it reacts with colored cations.
- Borax (Na2B4O7·10H2O) upon heating forms a glassy bead that can react with metal ions to produce a colored bead.

**Hint:** Think about the chemical reactions involved when borax is heated and how it interacts with different cations.

3. **Chemical Reaction:**
- When borax is heated, it decomposes to form sodium metaborate (NaBO2) and boron trioxide (B2O3).
- When a colored cation (like Co²⁺, Cu²⁺, or Fe³⁺) is introduced, it reacts with the borax glass to form a colored complex, resulting in a colored bead.

**Hint:** Identify the specific colors associated with different metal cations during the borax bead test.

4. **Conclusion:**
- Both the assertion and the reason are true. The assertion correctly states that colored cations can be identified using the borax bead test, and the reason correctly explains how the transparent bead interacts with colored cations to form a colored bead.
- Therefore, the assertion and reason are both true, and the reason provides a valid explanation for the assertion.

**Final Answer:** Both the assertion and reason are true, and the reason is the correct explanation of the assertion.

### Summary:
- Assertion: True (Colored cations can be identified by the borax bead test).
- Reason: True (Transparent bead forms colored bead with colored cation).
- Conclusion: Both assertion and reason are true, and the reason explains the assertion.