Isoelectronic species have the same number of

Which of the following gases has the lowest rate of diffusion?
[H=1.0, C=12.0, N = 14.0, O= 16.0]

An example of a crystalline substance that does not possess water of crystallization is

The best indicator to use for the titration of ethanoic acid with sodium hydroxide is

The relative molar mass of a gaseous hydrocarbon is 30. Determine its vapour density.