Observe the statements. I. Phenolphthalein is a colourless solution
II. Phenolphthalein turns pink in basic solution
III. Phenolphthalein turns red in acidic solution
IV. Phenolphthalein remains colourless in acidic solution
Choose the correct option
a. I &II are correct
b. I & III are correct
c. I ,II & IV are correct
d. All the statements are correct

the observation of the third option is correct one.

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.