$Y :$ The resistivity of a semiconductor decreases with increases of temperature.

$Z :$ In a conducting solid, the rate of collision between free electrons and ions increases with increase of temperature.

Select the correct statement from the following :

statement$-1$ : The temperature dependence of resistance is usually given as $R=R_{0}(1+\alpha \Delta t)$. The resistance of a wire changes from $100\; \Omega$ to $150\; \Omega$ when its temperature is increased from $27^{\circ} C$ to $227^{\circ} C$. This implies that $\alpha=2.5$ $\times 10^{-3} /{ }^{\circ} C$

statement$-2\;: R=R_{0}(1+\alpha \Delta t)$ is valid only when the change in the temperature $\Delta T$ is small and $\Delta R=\left(R-R_{0}\right) < < R_{0}$