which of these are redox reactions...?

Question

2 KClO3 -> 2 KCl + 3 O2
H2 + Cl2 -> 2 HCl
Zn + CuSO4 -> ZnSO4 + Cu
NH3 + HCl -> NH4+ + Cl-
C + O2 -> CO2
H2SO4 + 2 KOH -> K2SO4 + 2 H2O
2 H2O -> 2 H2 + O2
2 Na + Cl2 -> 2 NaCl
NaCl + AgNO3 -> AgCl + NaNO3

Answer 1

ALL of the reactions listed are classified as redox reactions
EXCEPT the following three:
NH3 + HCl (This is acid-base)
H2SO4 + KOH (also acid-base)
NaCl + AgNO3 (double replacement)

Answer 2

Redox equations involve an apparent change of valance in ions such that some are being increased in valance (oxidized) and others are being reduced. In the first reaction, the Clorate ion (ClO3)- , chlorine has the apparent state of +7 and oxygen -2. After decomposition, chloride ion has a -1 charged (it has been reduced), and oxygen has a 0 valance (oxygen has been oxidized !!).

Simple acid-base reactions, and displacement reactions dont fall into this category. So you can go through your collection, and rule these out.

Decomposition and formation reactions are redox reactions, and those you can figure out.