one of the properties of matter is density. density is defined as the mass per unit of volume of a substance. a substance that is more dense than another has more mass for the same volume than the other substance.

The more dense, the more easily it sinks to the ground.

Thank you @DrBob222

Hydrogen

It's chlorine 3.21

To determine which gas would most readily flow along the ground if accidentally released, we need to consider the relative densities of the gases listed.

Density is defined as the mass per unit of volume of a substance. In this case, the density values for the gases are given as follows:
- Chlorine: 3.21
- Ethyne: 1.17
- Helium: 0.18
- Hydrogen: 0.09
- Nitrogen: 1.25

The gas that would most readily flow along the ground would be the one with the lower density, as lower density indicates less mass for the same volume, making it lighter and more likely to disperse easily.

Looking at the options, we can see that the gas with the lowest density is hydrogen, with a density of 0.09. Therefore, option D - hydrogen, would be the gas that would most readily flow along the ground if accidentally released.

To determine this, we compared the density values for each gas and selected the one with the lowest value.