Question

Nitrogen dioxide gas turns moist blue litmus_____.
(A) white
(B) red
(C) yellow
(D) black

Answer 1

Hint: If litmus turns red, it means that in the test tube there is an acidic gas. This means that there is a pure elemental gas such as nitrogen in the tube if all forms of litmus paper fail to change color. Oxides of metals are basic while oxides of non-metals are acidic.

Complete step by step solution:
With filtered water, moisten a piece of red litmus paper. At different science supply stores, you can buy red litmus paper, and it's also sometimes available at pet or pool supply stores.
In a test tube, put your piece of moistened red litmus paper. Fill and stop the test tube with the gas that you want to test.
Wait a couple of minutes. It means that the test tube contains a simple gas if the red litmus paper turns blue. If the color of the paper does not change, then the tube does not have any simple gas. Then you can use blue litmus paper to repeat the test.
Determine which elemental gas is likely in the tube by first filling the gas you want to measure with a large flask with a wide bottom and narrow neck. Then light a match or splint and bring the lit portion into the flask and observe what happens by holding it at the end. If the flame is extinguished, then the tube has no oxygen, and the gas is one that has no fire reactivity, such as nitrogen. Nitrogen gas, since it is inert, has no fire reactivity. If no larger flasks are open, you can also drop a burning match into a standard test tube and observe the immediate reactions before the gas escapes.
The following reaction occurs when nitrogen dioxide reacts with water (wet),
 $ 2N{O_2} + {H_2}0 \to HN{O_2} + HN{O_3} $
Hence, option B-Red is the correct answer.

Note:
A majority of the Earth's atmosphere is composed of nitrogen oxide. It has no color and no scent, so you need to use a separate technique to search for its existence. Nitrogen gas may also be mixed to form compounds with other elements, such as nitrate ( $ N{O_3} $ ), nitrite ( $ N{O_2} $ ) and ammonium, for example ( $ N{H_3} $ ).