which is a redox reaction?

a. 2H Br+ Ba (OH)2 --> 2H2 O+ BaBr2
b. 2AIPO4 + 3Mg --> 2Al + Mg3 (PO4)2
c. HNo3 + NaOH --> H2O + NaNO3
d. NaCl + H2So4 --> Na2 SO4 + 2HCl