mujhe is baat p bahut hasi aaye

A(1-2-3-4) B(5-6-7-8) C(9-10-11-12)
FIRST WEIGHT – A(1-4) vs B(5-8)

(FIRST CASE) — both are equal then odd ball is in C(9-12)

second weighing: take 9-10-11 weight with any three balls in A & B

if equal then odd ball is 12 (in third weight will prove it’s heavier or lighter)

else odd ball is in 9-10-11 (now we know it’s heavy or light)
third weighing between any two of 9-10-11 balls, it will give u the odd ball.

(SECOND CASE) — Both are unequal then odd ball is in 1-8
but this will be clear that if odd ball is heavy then it will be in heavier side and if it is light then it is in lighter side
for convenience assume A(1-4) is lighter and B(5-8) is heavier.

second weighing take 1-5-6 vs 2-7-8
(now three cases)

if both are equal
then Odd ball is 3 or 4. Weight 3 with any other 10balls. If Equal then 4 is odd&lighter otherwise 3

if 1-5-6 is heavier
then odd ball is in 2 or 5 or 6. Weight 5 vs 6. If equal then 2 is odd&lighter else heavier is odd&heavier.

if 2-7-8 is heavier
then odd ball is in 1 or 7 or 8. Weight 7 vs 8. If equal then 1 is odd&lighter else heavier is odd&heavier.