A gas obeys the equation of state P(V-b) = RT (The parameter b is constant). The slope for an isochore will be:
Negative
Zero
R/(V-b)
R/P
P(V-b) = RT
P = RTV−b
P = ⟮RV−b⟯T+0
y = mx + c (y = P and x = T for isochore)
slope = RV−b