3 points
Pure N2? Probably rare. The solar system does have a shit ton of ammonia though, so thats a great source of nitrogen that can be broken down to get what we need.
I’d argue phosphorus is an even more limiting compound.
4 points
It is a regular enough mineralogical component in martian regolith. If we use the soil to grow things, we should be fine as is. Furthermore, we aren’t worried about losing it into space if we terraform.
On the scale of the solar system, phosphorus may indeed end up being rare and might be one of the limiting factors for total load bearing capacity of the solar system.
