which reaction is not a redox reaction a) KOH + HCl -> KCl + H2O b) 2K +Cl2 -> 2KCl?

Identifying reactions....

a) KOH + HCl -> KCl + H2O -- double replacement (acid-base neutralization) --- Not redox
b) 2K + Cl2 -> 2KCl -- synthesis --- Redox

Redox reactions are recognized by changes is oxidation state. There must be oxidation - an increase in oxidation state, and reduction - a decrease in oxidation state. In reaction (b) potassium is oxidized and chlorine is reduced.

a)
KOH + HCl → KCl + H₂O
This is NOT a redox reaction.
This is because there is no change in oxidation number.
Oxidation number of K in KOH/KCl = +1
Oxidation number of O in KOH/H₂O = -2
Oxidation number of H in KOH/HCl/H₂O = +1
Oxidation number of Cl in HCl/KCl = -1

b)
2K + Cl₂ → 2KCl
This is a redox reaction.
K is oxidized as the oxidation number of K increases from 0 (in K) to +1 (in KCl).
Cl₂ is reduced as the oxidation number of Cl decreases from 0 (in Cl₂) to -1 (in KCl).

...... The answer is : KOH + HCl → KCl + H₂O