When orthoboric acid is heated to red heat the residue is

Options

A. Boron
B. Boron oxide
C. Pyroboric acid
D. Metaboric acid

Explanation

To solve the question regarding the residue formed when orthoboric acid is heated to red heat, we can follow these steps:

### Step 1: Understand the Composition of Orthoboric Acid
Orthoboric acid is represented by the chemical formula H₃BO₃. It contains boron (B), oxygen (O), and hydrogen (H).

**Hint:** Remember the chemical formula of orthoboric acid and its components.

### Step 2: Heating Orthoboric Acid
When orthoboric acid is heated, it undergoes a thermal decomposition process. Initially, at a temperature around 375 K (approximately 102 °C), orthoboric acid loses water and converts to metaboric acid (HBO₂).

**Hint:** Consider the temperature range and the products formed during the initial heating.

### Step 3: Further Heating to Red Heat
If the heating continues to a higher temperature, specifically to red heat (which is around 600 °C or more), metaboric acid (HBO₂) further decomposes to form boron trioxide (B₂O₃).

**Hint:** Think about the conditions needed for further decomposition and the resulting products.

### Step 4: Identify the Residue
The final product after heating orthoboric acid to red heat is boron trioxide (B₂O₃), which is also referred to as boron oxide or boric anhydride.

**Hint:** Recall the common names for boron trioxide and its significance as a residue.

### Conclusion
When orthoboric acid is heated to red heat, the residue formed is boron trioxide (B₂O₃).

### Final Answer
The residue formed when orthoboric acid is heated to red heat is boron trioxide (B₂O₃).

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