Answer
(a) greater than
(b) II
Work Step by Step
(a) We know that
$T=\frac{m_ac_aT_a+m_wc_wT_w}{m_ac_a+m_wc_w}$
We plug in the known values to obtain:
$T=\frac{(0.5Kg)c_a(20C^{\circ})+(0.5Kg)(2c_a)(30C^{\circ})}{(0.5Kg)(c_a)+(0.5Kg)(2c_a)}=30C^{\circ}$
Thus, the final temperature of the mixture of water and alcohol is greater than $25C^{\circ}$.
(b) We know that the best explanation is option (II) -- that is, more heat is required to change the temperature of water than to change the temperature of alcohol. Therefore, the final temperature will be greater than $25C^{\circ}$
