What is the term used as correction for attractive forces in the Van der Waals Equation? I have seen a question in my textbook which is little bit confusing,

The term that corrects for attractive forces present in real gas in van der Waal equation is
(i) ${nb}$ 
(ii) $\frac{an^2}{V^2}$ 
(iii) $\frac{-an^2}{V^2}$ 
(iv) ${-nb}$

Since the question is about term  &quot;forces&quot; I do not see any of the four options dimensionally correct as (i)&amp;(iv) are related to volume and (ii)&amp;(iii) are related to pressure.
But in my textbook answer the correct answer given is (ii) so how is it dimensionally correct?
Nothing states that the correction is itself a force, only that the correction is for attractive forces. There is thus no need for the correction to have the dimensions of a force.