Calculate the temperature change of a 1 cm³ object if its volume expands by 0.0018 cm³ given a linear expansivity of 2.0 x 10⁻⁵ K⁻¹.

For an isotropic material, the volume expansivity is approximately three times the linear expansivity:

$$\gamma = 3\alpha$$ $$\gamma = 3 \times (2.0 \times 10^{-5} \, \text{K}^{-1})$$ $$\gamma = 6.0 \times 10^{-5} \, \text{K}^{-1}$$

$$\Theta = \frac{0.0018 \, \text{cm}^3}{(6.0 \times 10^{-5} \, \text{K}^{-1})(1 \, \text{cm}^3)}$$ $$\Theta = \frac{0.0018}{6.0 \times 10^{-5}} \, \text{K}$$ $$\Theta = \frac{1.8 \times 10^{-3}}{6.0 \times 10^{-5}} \, \text{K}$$ $$\Theta = 0.3 \times 10^{(-3 - (-5))} \, \text{K}$$ $$\Theta = 0.3 \times 10^2 \, \text{K}$$ $$\Theta = 30 \, \text{K}$$

Since a change in temperature of $1 \, \text{K}$ is equivalent to a change of $1 \, ^\circ\text{C}$, the temperature change is $30 \, ^\circ\text{C}$.

Comparing this to the given options:
(A) $25^\circ\text{C}$
(B) $20^\circ\text{C}$
(C) $30^\circ\text{C}$
(D) $50^\circ\text{C}$

The calculated value matches option (C).

The final answer is \boxed{\text{(C) 30^\circ C}}