The highest pressure gas of a mixture has partial pressure p, the partial pressure of other gases decreases by factor of 2n-1, the partial pressure of second gases decreases by a factor of 2, partial pressure of third gas increases by 4, and so on, if the total pressure of gas mixture is 31p/16, how many gases are present in the mixture?

Correct Answer: 5
Let n gases are present in the mixture, => p + p/2 + p/4 + – – – + p/2n-1 = 7p/8, => p(1 – 1/2n)/(1 – ½) = 31p/16, => n = 5.