Isochores are drawn at

What is the relative rate of diffusion of a gas (molecular weight = $98$) compared to hydrogen?

$A$ sample of $O_2$ gas is collected over water at $23\,^oC$ and a barometric pressure of $751\,mm\,Hg$. What is the partial pressure of the $O_2$ gas in this sample? (Vapor pressure of water at $23\,^oC$ is $21\,mm\,Hg$)

Helium is added to the oxygen supply used by deep sea divers because

$A$ neon-dioxygen mixture contains $70.6 \ g$ dioxygen and $167.5 \ g$ neon. If the total pressure of the mixture of gases in the cylinder is $25 \ bar$,what are the partial pressures of dioxygen and neon in the mixture?

List the different units of gas pressure.