Water is moving across a membrane from solution a into solution b. what can be inferred? solution a must be pure water. solution a must have a lower solute concentration than solution b. solution a must have a higher solute concentration than solution b. solution a and solution b must have the same concentration of solutes. solution b must be pure water.

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.

"the periodic table is arranged in order of atomic number."

the volume increases