Solution: The statement says that two blocks are present on a lid of a container with volume of 9 m³. The mass of lid is equal to the mass of two blocks. It means that initially there are four blocks (or four atm pressure) upon 9 m³ volume.
After that four more blocks are placed on the lid. Means the pressure is increased from 4 atm to 8 atm (2 atm of lid, 2 atm of old blocks, 4 atm of new four blocks).
Crude oil is mixture (solution) consist of several different hydrocarbons (alkanes, alkenes...). This hydroalkanes can be separated from mixture (crude oil) using distilation (usually fractional distillation), because they have different boiling points.
Proportion of hydrocarbons is diiferent in varios parts of the world.
Solution is homogeneous mixture composed of two or more substances.
A. 2Br+Cl2=2BrCl B. Is balanced C. 2 goes in front of NaCl D. 2ZnS+3O2=2ZnO+2SO2 E. 2 in front of KBr and KCl F. 2 goes in front of NaOH and H2O Balance equations calculator on the internet will help with this