(just want to check my answer)

what fact is the most important indicator that the following reaction will take place?

ni(no3)2)aq) + k2s(aq) nis(s) + 2kno3(aq)

a) the reaction is a double displacement *my answer*
b) a precipitate is formed.
c) the reactants are ionic compounds.
d) the products are ionic compounds.

Observation and experimentation have led many scientists to accept a theory about the origin of the universe. this theory is called the big bang theory. scientific evidence collected and observed by scientists around the world suggests that the universe is ever expanding from a hot and dense initial state. what makes this a scientific theory? (2 points)