Chemistry - PV=nRT approximation on other planets?

The differences in acceleration due to gravity is not the main factor in comparing how accurate the approximation is for each planet.

The main factor is the mass of gas each planet's atmosphere contains.

Mercury has almost no atmosphere. The total mass of all gas in Mercury's atmosphere is only 10000 kg! The pressure is less than $10^{-14}$ bar. The approximation will be very accurate.

The mass of Venus's atmosphere is $4.8 \times 10^{24}$kg and pressure is 92 bar, so PV = nRT will be much worse of an approximation than on earth.

Mars has a small atmosphere, less than Earth more than Mercury.

Jupiter, Saturn, Uranus and Neptune are gas giants with no distinct surface.