<u>Answer:</u> The molality and molarity of zinc in the solution is 4.07 m and 28.11 M respectively.
<u>Explanation:</u>
Solute is the substance which is present in smaller proportion in a mixture and solvent is the substance which is present in larger proportion in a mixture.
We are given:
(m/m) % of Cu = 79 %
This means that 79 g of copper is present in 100 grams of alloy.
(m/m) % of Zn = 21 %
This means that 21 g of zinc is present in 100 grams of alloy.
As, zinc is present in smaller proportion. So, it is solute and copper is the solvent.
- <u>Calculating molality of zinc:</u>
To calculate molality of the zinc, we use the equation:

where,
 = Given mass of solute (Zinc ) = 21 g
 = Given mass of solute (Zinc ) = 21 g
 = Molar mass of solute (Zinc) = 65.3 g/mol
 = Molar mass of solute (Zinc) = 65.3 g/mol
 = Mass of solvent (copper) = 79 g
 = Mass of solvent (copper) = 79 g
Putting values in above equation, we get:

- <u>Calculating molarity of zinc:</u>
To calculate volume of a substance, we use the equation:

Density of solution = 
(Conversion factors used are:  1 kg = 1000 g &   )
  )
Mass of solution = 100 g
Putting values in above equation, we get:

To calculate the molarity of solution, we use the equation:

We are given:
Molar mass of zinc = 65.3 g/mol
Volume of solution =  (Conversion factor:
     (Conversion factor:   )
  )
Mass of zinc = 21.0 g
Putting values in above equation, we get:

Hence, the molality and molarity of zinc in the solution is 4.07 m and 28.11 M respectively.