Acylinder contains 4.0 g of nitrogen gas. a piston compresses the gas to half its initial volume. afterward, by what factor has the mass density of the gas increased?

The mass density will be doubled

Explanation:

Density is given by dividing the mass of a substance by its volume.An increase in mass causes an increase in density and vice versa, while a  decrease in volume causes an increase in density and volume.Therefore, when the volume is halved, then the density will be doubled if the mass is kept constant.This has no effect on the number of moles as the mass is constant.