http://i67.tinypic.com/6iek47.jpg - Question 30 why is the answer (a)..?

Refer to the graph. The initial pH 7 indicates that the water is neutral before gas Y is bubbled. When time goes by, the pH becomes greater than 7. This indicates that Y is a basic gas which dissolves in water to form an alkaline solution.

Among the four options, ammonia (A) is basic, hydrogen (B) is neutral, while carbon dioxide (C) and hydrogen chloride (D) are acidic.

...... The answer is: A. ammonia