In which solution will thymol blue indicator appear blue?
(1) 0.1 m ch3cooh (3) 0.1 m hcl
(2) 0.1 m koh (4) 0.1 m h2so4

(2) 0.1 M KOH

Explanation:

Thymol blue is an universal indicator. Thymol blue has a blue color when in basic conditions (pH > 7), a green color in neutral conditions (pH =7), and a yellow color in acidic conditions (pH < 7).

pH or pOH is the measure of acidity or alkalinity of a solution.  pH is calculated by taking negative logarithm of hydrogen ion concentration.

0.1 M ,  0.1 M  and  0.1 M are all acidic in nature.

Thus thymol blue will appear blue in basic 0.1 M KOH.