On burning magnesium ribbon in air, it is observed that

Options

A. a greenish gas is obtained
B. it burns brightly, giving golden colour
C. it burns brightly, leaving a blue ash
D. it burns brightly, leaving behind a white powder

Explanation

To answer the question about what is observed when burning magnesium ribbon in air, we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding the Reaction**: When magnesium ribbon is burned in air, it undergoes a combustion reaction. The primary reactant is magnesium (Mg), and the main component of air that supports combustion is oxygen (O₂).

2. **Combustion of Magnesium**: The magnesium reacts with oxygen in the air. The chemical equation for this reaction is:
\[ 2Mg + O_2 \rightarrow 2MgO \]
This shows that two moles of magnesium react with one mole of oxygen to produce two moles of magnesium oxide (MgO).

3. **Observation of Flame**: When magnesium burns, it produces a bright, dazzling white flame. This is a characteristic feature of magnesium combustion.

4. **Formation of Magnesium Oxide**: The product of the combustion is magnesium oxide, which appears as a white powder. This powder is formed as the magnesium ribbon burns and reacts with the oxygen.

5. **Heat Release**: The combustion of magnesium is an exothermic reaction, meaning it releases a large amount of heat. This is why the flame is so bright and intense.

6. **Final Observations**: Therefore, when magnesium ribbon is burned in air, it is observed that:
- A bright white flame is produced.
- A white powder (magnesium oxide) is left behind.
- A large amount of heat is released.

### Conclusion:
The key observations when burning magnesium ribbon in air are:
- A dazzling white flame is produced.
- White powder (magnesium oxide) is formed.
- A significant amount of heat is released.