Chapter 4.4, Problem 1RCF

Which of the following combination reactions is not a redox reaction?

(a)     $2\text{Mg}(s)+{\text{O}}_2(g)\to 2\text{MgO}(s)$

(b)     ${\text{H}}_2(g)+{\text{F}}_2(g)\to 2\text{HF}(g)$

(c)     ${\text{NH}}_3(g)+\text{HCl}(g)\to {\text{NH}}_4\text{Cl}(s)$

(d)     $2\text{Na}(s)+\text{S}(s)\to {\text{Na}}_2\text{S}(s)$