Which of the following statements are true regarding diamond?

Options

A. It is the hardest substance
B. It has three dimensional structure
C. It is a good conductor of heat and electricity
D. It is used in jewellery and for cutting glass and drilling rocks.

Answer

To determine which statements are true regarding diamond, let's analyze each statement one by one.

### Step 1: Analyze Statement A
**Statement A:** "Diamond is the hardest substance."
- Diamond is indeed known as the hardest natural substance on Earth. This statement is true.

### Step 2: Analyze Statement B
**Statement B:** "It has a three-dimensional structure."
- Diamond has a giant three-dimensional network structure where each carbon atom is tetrahedrally bonded to four other carbon atoms. This statement is also true.

### Step 3: Analyze Statement C
**Statement C:** "It is a good conductor of electricity."
- Diamond is a poor conductor of electricity because it lacks free electrons. This statement is false.

### Step 4: Analyze Statement D
**Statement D:** "It is used in jewelry and for cutting glasses and drilling rocks."
- Due to its hardness and brilliant appearance, diamond is widely used in jewelry. Additionally, its hardness makes it suitable for cutting glass and drilling rocks. This statement is true.

### Conclusion
The true statements regarding diamond are:
- Statement A: True
- Statement B: True
- Statement C: False
- Statement D: True

Thus, the correct statements about diamond are A, B, and D.

---