Without consulting App. D$,$ predict the sign of the entropy change $(\frac{?}{{?}_{\frac{?}{?}}S})$ for the following processes:

$($a$)Ar(g,600K)Ar(g,200K)$ at $1$atm

$($b$)2N{H}_{4}Cl{O}_4(s)N_2(g)+C{l}_2(g)+4H_{2}O(g)+2O_2($g$)$ at $400K$ and $4$atm

$($c$)P_4(g)2P_2($g$)$ at $298\mathrm{.}15K$ and $1$atm

$($d$)C_6{H}_{5}C{H}_3(g)C_6{H}_{5}C{H}_3(l)$ at $298\mathrm{.}15K$ and $1$atm