The reason(s) why aluminium is preferred over copper for making overhead transmission cables
(i) Aluminium is lighter than copper
(ii) aluminium is harder than copper
(iii) aluminium is less soluble in water than copper.

Options

A. Only (i)
B. Only (iii)
C. Only (i) and (ii)
D. (i), (ii) and (iii)

Explanation

To answer the question of why aluminum is preferred over copper for making overhead transmission cables, we can analyze each of the given statements step by step.

### Step 1: Analyze the first statement
**Statement (i): Aluminum is lighter than copper.**
- This statement is true. Aluminum has a lower density (approximately 2.7 g/cm³) compared to copper (approximately 8.96 g/cm³). This makes aluminum significantly lighter than copper, which is a crucial factor for overhead transmission cables as it reduces the load on the supporting structures.

### Step 2: Analyze the second statement
**Statement (ii): Aluminum is harder than copper.**
- This statement is misleading. While aluminum can be made harder through alloying and treatment, in general, copper is actually tougher and more ductile than aluminum. The hardness of a material is not a primary factor in the choice of material for overhead cables, as flexibility and weight are more critical.

### Step 3: Analyze the third statement
**Statement (iii): Aluminum is less soluble in water than copper.**
- This statement is somewhat irrelevant in the context of overhead transmission cables. Both metals have low solubility in water, and the solubility of metals is not a significant factor when it comes to their use in cables. The cables are typically insulated to prevent any interaction with water.

### Conclusion
From the analysis:
- Only the first statement (i) is correct. Aluminum is preferred over copper for overhead transmission cables primarily because it is lighter, which is essential for reducing the load on the supporting structures. The other two statements do not provide valid reasons for the preference of aluminum over copper in this application.

### Final Answer
**Correct Answer: Only statement (i) is correct.**