On the second thought - question is no clear. It doesn't state anything about temperature. If the idea is that it is measured at STP many substances are ruled out, even if they have (in their temperature range) much higher expansion ratio.
And neon doesn't look to me like a possible record holder (even for elemental substances at STP). For example xenon seems to be a tiny bit better (and I am not stating it is Xe that wins in this category).
This is still not clear. You can't compare water (boils at 100 deg C) with iron (boils around 2900 deg C) even if they can be both converted to gaseous form. For obvious reasons 1 mole of gas at 2900 deg C will have much higher volume.
The problem hasn't gone away - gases expand a lot more with temperature than liquids do, so liquids with higher boiling points are likely to score higher on your scale. Knowing the purpose and constraints would certainly help us a lot.
You can certainly google for whatever info you want and build a table of whatever you really want, though.
We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling We Value Civility
• Positive and compassionate attitudes
• Patience while debating We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving