Relative density of a liquid is 0.8. What its density in (i) C.G.S. system (ii) S.I. unit.

Explanation

To find the density of a liquid given its relative density, we can use the following steps:

### Step 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 a reference substance, typically water. The formula is:
\[ \text{Relative Density} = \frac{\text{Density of Liquid}}{\text{Density of Water}} \]

### Step 2: Identify the density of water in different systems
- In the C.G.S. (Centimeter-Gram-Second) system, the density of water is approximately \(1 \, \text{g/cm}^3\).
- In the S.I. (International System of Units) system, the density of water is approximately \(1000 \, \text{kg/m}^3\).

### Step 3: Calculate the density of the liquid in the C.G.S. system
Given that the relative density of the liquid is \(0.8\):
\[ \text{Density of Liquid} = \text{Relative Density} \times \text{Density of Water} \]
Substituting the values for the C.G.S. system:
\[ \text{Density of Liquid} = 0.8 \times 1 \, \text{g/cm}^3 = 0.8 \, \text{g/cm}^3 \]

### Step 4: Calculate the density of the liquid in the S.I. system
Using the same formula for the S.I. system:
\[ \text{Density of Liquid} = \text{Relative Density} \times \text{Density of Water} \]
Substituting the values for the S.I. system:
\[ \text{Density of Liquid} = 0.8 \times 1000 \, \text{kg/m}^3 = 800 \, \text{kg/m}^3 \]

### Final Answers:
(i) The density of the liquid in C.G.S. system is \(0.8 \, \text{g/cm}^3\).

(ii) The density of the liquid in S.I. unit is \(800 \, \text{kg/m}^3\).

---