To determine the number of moles of air present in the tank, we assume that air is an ideal gas in order for us to use the following equation, n = PV/RT Substituting the known values, n = (195 atm)(350 L) / (0.0821 L.atm/mol.K)(10 + 273.15 K) n = 2935.91 moles Thus, the number of moles of air is approximately 2935.91 moles.
So, litmus paper is a qualitative tool for assessing the acidity or basicity of a substance (usually a solution). In general, blue litmus turns red in the presence of an acid, and red litmus turns blue in the presence of a base. They can't really tell you much more than that.
The solutions that are most likely acids are those that turn blue litmus red <em>and </em>do not evoke a color change in red litmus. A solution that turns red litmus blue <em>or </em>does not evoke a color change in blue litmus is likely not an acid. Using these criteria, solutions 4 and 7 are most likely acids since they both turn blue litmus red (and they cause no color change in red litmus).