At constant pressure, which of these systems do work on the surroundings? check all that apply.

1. 2a(g) + 2b(g) > 5c(g)
2. a(g) + 2b(g) > 2c(g)
3. 2a(g) + b(s) > 3c(g)
4. 2a(g) + 2b(g) > 3c(g)

I am pretty sure that the systems which work on the surroundings are :
A. 2A(g) + 2B(g) > 5C(g)
 B. A(g) + 2B(g) --->2C(g)
Since B is a solid, A incrases (2-3) so it is an expansion. The same happens with B from 4 to 5 moles of C. I thing is clear, and I hope you will find it helpful.

Yes you are correct use the scientific method