<u>Answer:</u>
(a): The balloon will contain 
number of molecules now.
(b): The gas law associated with this is Avogadro's law.
<u>Explanation:</u>
Avogadro's law states that the volume of the gas is directly proportional to the number of moles of the gas at constant pressure and temperature
Mathematically,
(At constant pressure and temperature)
OR
.....(1)
where,
= Initial volume and number of moles
= Final volume and number of moles
We are given:
Putting values in equation 1, we get:
(a):
If 
number of moles of gas contains X number of molecules
So, 
number of moles of gas will contain = 
number of molecules
Hence, the balloon will contain number of molecules now.
(b): The law used is Avogadro's law.
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Formula for pH is pH = -log [H+]
you use 4.0x10^-9 and substitute in for [H+]
Fromula looks like this:
pH = -log (4.0x10^-9) - from here different calculators will require different buttons to push to get the answer
Solved out:
pH = -log (4.0x10^-9)
pH = -(-8.398) = 8.398 is the pH
More acid solution has red colour, more basic solution has purple colour whereas neutral solution has green colour.
<h3>Which color represents the most acidic solution?</h3>
As the solution becomes more acidic, the color of the solution changes from green toward red.
<h3>Which color represents the most basic solution?</h3>
As the solution becomes more basic, the color changes of the solution from green toward purple.
<h3>Which color represents a neutral solution?</h3>
Green color of the solution represents a neutral solution having pH 7.
So we can conclude that More acid solution has red colour, more basic solution has purple colour whereas neutral solution has green colour.
Learn more about acid here: brainly.com/question/25148363
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