Resistance , R = 0.84Ω
Length of wire , L = 1m
diameter of circular part of wire ,d = 0.2m
so, base area of wire , A = πr² = πd²/4 [ ∵d = 2r]
= 3.14 × (0.2)²/4m²
= 3.14 × 0.04/4 m²
= 0.1256/4 m² = 0.0314 m²
Now, use formula, 
R = ρL/A 
Here, R is the resistance, ρ is the resistivity , L is the length of wire and A is the base area of it 

So , ρ = RA/L = 0.84Ω × 0.0314m²/1m
ρ = 2.6376 × 10⁻² Ωm 
Hence, resistivity is 2.6376 × 10⁻²Ωm at 20 degree C.

**Calculation of Resistivity of a Metal Wire**

To calculate the resistivity of a metal wire, we need to use the formula:

R = (ρ * L) / A

Where:
- R is the resistance of the wire
- ρ (rho) is the resistivity of the material
- L is the length of the wire
- A is the cross-sectional area of the wire

**Given Data:**
- Length of the wire (L) = 1 m
- Resistance of the wire (R) = 0.84 Ω
- Diameter of the wire (d) = 0.2 m

**Calculating the Cross-Sectional Area:**

The cross-sectional area of a wire can be calculated using the formula:

A = π * (d/2)^2

Where:
- A is the cross-sectional area
- d is the diameter of the wire

Substituting the given values, we have:

A = π * (0.2/2)^2
A = π * (0.1)^2
A = π * 0.01
A = 0.0314 m^2

**Calculating the Resistivity:**

Now, we can rearrange the formula to solve for resistivity (ρ):

ρ = (R * A) / L

Substituting the given values, we have:

ρ = (0.84 * 0.0314) / 1
ρ = 0.026376 Ω.m

Therefore, the resistivity of the metal wire is 0.026376 Ω.m.

**Explanation:**

The resistivity (ρ) is a fundamental property of a material that characterizes its ability to resist the flow of electric current. It is a measure of how strongly a material opposes the flow of electrons.

In this calculation, we used the formula for resistance of a wire to determine its resistivity. The resistance of a wire depends on its length (L), cross-sectional area (A), and the resistivity of the material (ρ). By rearranging the formula and substituting the given values for resistance, length, and cross-sectional area, we can solve for the resistivity.

The cross-sectional area is calculated using the diameter of the wire. Since the diameter is given, we can use the formula for the area of a circle to calculate the cross-sectional area.

Once we have the cross-sectional area and resistance, we can substitute them into the formula for resistivity to calculate the value.

It's important to note that resistivity is a property that is specific to each material and can vary depending on temperature and other factors. In this case, the resistivity was calculated at a temperature of 20°C.