Given data

• Length of copper rod: $L_{\text{Cu}} = 25\text{ cm} = 0.25\text{ m}$
• Length of aluminium rod: since it is a similar rod, $L_{\text{Al}} = 0.25\text{ m}$
• Cross-sectional area of each rod: $A = 3\text{ mm}^2 = 3 \times 10^{-6}\text{ m}^2$
• Resistivity of copper: $\rho_{\text{Cu}} = 1.7 \times 10^{-8}\ \Omega\text{m}$
• Resistivity of aluminium: $\rho_{\text{Al}} = 2.6 \times 10^{-8}\ \Omega\text{m}$

Interpretation of the combination

The copper rod is joined end-to-end with the aluminium rod, so they are in series between ends $A$ and $B$.

Therefore, $R_{AB} = R_{\text{Cu}} + R_{\text{Al}}$

Resistance of copper rod

Using $R = \rho \frac{L}{A}$

$R_{\text{Cu}} = 1.7 \times 10^{-8} \times \frac{0.25}{3 \times 10^{-6}}$

$R_{\text{Cu}} = \frac{1.7 \times 0.25 \times 10^{-8}}{3 \times 10^{-6}}$

$R_{\text{Cu}} = \frac{0.425 \times 10^{-8}}{3 \times 10^{-6}}$

$R_{\text{Cu}} = 1.4167 \times 10^{-3}\ \Omega$

$R_{\text{Cu}} \approx 1.417\text{ m}\Omega$

Resistance of aluminium rod

$R_{\text{Al}} = 2.6 \times 10^{-8} \times \frac{0.25}{3 \times 10^{-6}}$

$R_{\text{Al}} = \frac{2.6 \times 0.25 \times 10^{-8}}{3 \times 10^{-6}}$

$R_{\text{Al}} = \frac{0.65 \times 10^{-8}}{3 \times 10^{-6}}$

$R_{\text{Al}} = 2.1667 \times 10^{-3}\ \Omega$

$R_{\text{Al}} \approx 2.167\text{ m}\Omega$

Total resistance

$R_{AB} = 1.4167 \times 10^{-3} + 2.1667 \times 10^{-3}$

$R_{AB} = 3.5834 \times 10^{-3}\ \Omega$

$R_{AB} = 3.583\text{ m}\Omega$

Compare with options

The calculated answer is: $3.583\text{ m}\Omega$

This does not match any given option.

Checking the stored answer

Stored correct answer is C: $0.858\text{ m}\Omega$, but this is not consistent with the standard series combination calculation.

In fact:

• Option B ($1.420\text{ m}\Omega$) is approximately only the resistance of the copper rod.
• Option D ($2.170\text{ m}\Omega$) is approximately only the resistance of the aluminium rod.
• Option C ($0.858\text{ m}\Omega$) is not obtained from the given data by any standard series/parallel interpretation for two similar rods joined end-to-end.

Hence, the provided options or figure likely contain an error/missing detail.