<u>Answer:</u> The concentration of the solution is 0.25 M
<u>Explanation:</u>
Let the volume of solution of 2.5 M NaCl be 10 mL
We are given:
Dilution ratio = 1 : 10
So, the solution prepared will have a volume of = 
To calculate the molarity of the diluted solution, we use the equation:
where,
are the molarity and volume of the concentrated NaCl solution
are the molarity and volume of diluted NaCl solution
We are given:
Putting values in above equation, we get:

Hence, the concentration of the solution is 0.25 M
Explanation:
If the density of the object is more than that of water, it will sink. Otherwise it will float. The density of water is 1 g/mL.
Substance 1,
Mass, m = 450 g, Volume, V = 90 mL
Density = mass/volume
So,

It will sink.
Substance 2,
Mass, m = 35 g, Volume, V = 70 mL
Density = mass/volume
So,

It will float.
Substance 3,
Mass, m = 24 g, Volume, V = 12 mL
Density = mass/volume
So,

It will sink.
Random motion of molecules produces a concentration gradient and a net movement of solute as random movement of molecules causes diffusion that causes movement of molecules from high concentration to low concentration . No ATP is required in this process. This causes movement of solute molecules and causes concentration gradient.