15.3 of an unknown substance was found to contain 0.15 moles. calculate the relative formula mass of the substance.

M_r = 100

Molar mass = grams/moles = 15.3 g/0.15 mol = 100 g/mol

∴ M_r = 100

Note: The answer can have only two significant figures because that is all you gave for the number of moles.

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.