james created a salt water solution by adding a scoop of the solute, salt, to a beaker of the solvent, water. after all the salt dissolves, james places the beaker of salt water on a hot plate and begins to heat the solution. after half of the water evaporates, the concentration of the solution has
a) increased.
b) decreased.
c) stayed the same.
d) it is impossible to tell without measuring.

The correct answer is A.

Explanation: Concentration is defined as the moles of solute present in 1 liter of solution.

Mathematically,

Here, James has placed a solution of salt in water on a hot plate. By placing the solution on a hot plate, evaporation of water is occurring which results in the decreases of the volume of the solution. As this happens, the denominator of the fraction decreases, which results in the increase of concentration.

Hence, the correct option is A.

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e