As the [H'] in a solution decreases, what happens to the [OH-]? OA.
It increases and the pH increases.
OB.
It increases and the pH decreases.
O C.
It increases and the pH stays constant.
OD.
It decreases and the pH increases.
O E
It decreases and the pH decreases.

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.