If the density of iron is `7900 "kg m"^(-3)` , then its relative density is

Options

A. `790`
B. `79`
C. `7.9`
D. `0.79`

Explanation

To find the relative density of iron given its density, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Relative Density**:
Relative density (also known as specific gravity) is defined as the ratio of the density of a substance to the density of water at 4 degrees Celsius.

2. **Identify the Given Values**:
- Density of iron = \(7900 \, \text{kg/m}^3\)
- Density of water at 4 degrees Celsius = \(1000 \, \text{kg/m}^3\)

3. **Use the Formula for Relative Density**:
The formula for relative density is:
\[ \text{Relative Density} = \frac{\text{Density of Object}}{\text{Density of Water}} \]

4. **Substitute the Values into the Formula**:
Substitute the density of iron and the density of water into the formula:
\[ \text{Relative Density} = \frac{7900 \, \text{kg/m}^3}{1000 \, \text{kg/m}^3} \]

5. **Perform the Calculation**:
- When you divide \(7900\) by \(1000\):
\[ \text{Relative Density} = 7.9 \]

6. **State the Result**:
The relative density of iron is \(7.9\). Since relative density is a ratio, it has no units.

### Final Answer:
The relative density of iron is \(7.9\).

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