Which of the following would have the slowest rate of diffusion at a given temperature

o2
ne
cl2
he

Chlorine will have the slowest rate of diffusion because it has the highest   relative molecular mass of 71 followed by O₂ with 32, then Neon 20 then He with 2

The rate of diffusion of a gas is inversely proportional to the square root of its relative molecular mass.  

out of these options:

ability to burn paper

pure sodium reacting violently with water

the boiling point of water

helium does not tend to react with anything

i would say this is a physical property:

helium does not tend to react with anything

why? :

i said helium does not tend to react with anything because well, it reacts to ! but ability to burn paper, pure sodium reacting violently with water, & the boiling point of water are chemical or

physical properties: the properties of a substance that can be observed without changing the chemical makeup of the substance

chemical properties: properties of a substance relating to the chemical nature and reactivity of the substance