PH của dd HCl 2.10-4M và H2SO4 4.10-4M:
A. 3
B. 4
C. 3,7
D. 3,1

The question is incomplete. complete question is attached belowanswer: correct answer is option b  i.e.  solid particles  reason: filter paper has small pores, through which smaller particles can pass through. however, solid particles  have relatively larger size. hence, they are least likely to pass through.

If your on odysseyware i believe the answer would be c. 

The answer is a. that is an exothermic reaction which means it produces heat