Ammonia is a basic compound. A basic substance turns red litmus paper blue, which is a common property of bases. Litmus is a pH indicator used to test the acidity or basicity of a solution.
Now, let’s analyze the options:
A. Red litmus to blue – This is correct because ammonia is basic and will turn red litmus paper blue.
B. Blue litmus to red – This is incorrect because only acids turn blue litmus paper red.
C. White litmus to red – This is incorrect because there is no white litmus paper used in such reactions.
D. White litmus to blue – This is also incorrect because white litmus paper is not used in these tests.
Therefore, the correct answer is A. Red litmus to blue.