Question

Which of the following chemical reactions is an oxidation-reduction reaction?  (3 points)
CuSO4 + BaCl2  BaSO4 + CuCl2
Pb(NO3)2 + 2NaCl  PbCl2 + 2NaNO3
N2 + 3H2  2NH3
K2SO4 + BaCl2  BaSO4 + 2KCl

Answer 1

in this kind of problems all you need to do is to write oxidation states of all atoms in equations and you will see in which reaction there is a change in oxidation state and thus you will know which one is red-ox reaction.
in your case answer is:
N2 + 3H2 --> 2NH3
because N2 and H2 change from oxidation state 0 to +1 hydrogen, and -3 nitrogen.