Because chloride is more reactive than hydrogen.
The answer is solution a must have a lower solute concentration than solution b.
That is when water is moving across a membrane from solution a into solution b, then solution a must have a lower solute concentration than solution b.
When solution a have a lower solute concentration than solution b, then water moves across a membrane from solution a into solution b.
A mixture is a portion of matter made up of two or more substances called constituents. Mixtures are the product of the mechanical joining of substances without change in chemical nature, and therefore, each constituent retains its properties.
the option 4