Question

What do you observe when moist blue litmus paper and moist red litmus papers are introduced in the jar of hydrogen?

Answer 1

changes colour red∆blue

When it is exposed to a basic compound, the hydrogen ions react with the added base. The conjugate base, formed from the litmus acid, has a blue color, so the wet red litmus paper turns blue in alkaline solution

Answer 2

they change colour in order to acidic or basic nature of that hydrogen containing jar.