Assertion: Magnesium does not impart characteristic colour to the bunsen-burner flame.
Reason: Ionisation energy of Mg is very high.

Options

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

Answer

To solve the question regarding the assertion and reason provided, we can break it down into clear steps:

### Step 1: Understand the Assertion
The assertion states that "Magnesium does not impart characteristic color to the Bunsen-burner flame." This means that when magnesium is heated in a flame, it does not produce a visible color that is typically associated with flame tests for other elements.

**Hint:** Recall that flame tests are used to identify the presence of certain metal ions based on the color they emit when heated.

### Step 2: Understand the Reason
The reason given is that "Ionisation energy of Mg is very high." Ionization energy is the energy required to remove an electron from an atom. A high ionization energy means that it is difficult to remove an electron from magnesium.

**Hint:** Consider how ionization energy affects the ability of an element to form ions and how this relates to the emission of light during a flame test.

### Step 3: Relate Assertion to Reason
To determine if the assertion is true and if the reason correctly explains it, we need to connect the two statements. The reason indicates that magnesium has a high ionization energy, which implies that it is less likely to lose an electron and form excited states that would emit light in a flame test.

**Hint:** Think about how the stability of an atom's electron configuration influences its behavior in a flame test.

### Step 4: Conclusion
Since magnesium has a high ionization energy, it does not easily lose electrons to enter excited states that would emit characteristic colors. Therefore, the assertion is true, and the reason correctly explains why magnesium does not impart a characteristic color to the flame.

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

### Summary of Steps:
1. Analyze the assertion about magnesium and flame color.
2. Understand the significance of high ionization energy.
3. Connect the assertion and reason logically.
4. Conclude that both statements are true and related.