Initial length (L₁) = 20 cm

Initial temperature = 10°C

Final temperature = 110°C

Rise in temperature (ΔT) = 110 − 10 = 100°C

Volume expansion coefficient (γ) = 36 × 10⁻⁶ /°C

Linear expansion coefficient (α) = \frac{\gamma}{3}

= \frac{36 \times 10^{-6}}{3}

= 12 × 10⁻⁶ /°C

Using the formula, L₂ = L₁ (1 + αΔT)

L₂ = 20 (1 + 12 × 10⁻⁶ × 100)

L₂ = 20 (1 + 0.0012)

L₂ = 20 × 1.0012

L₂ = 20.024 cm

Hence, the length of the iron rod at 110°C is 20.024 cm.