The concentration of solution in M or mol/L can be calculated using the following formula:
.... (1)
Here, n is number of moles and V is volume of solution in L.
The molecular formula of potassium sulfate is
thus, there are 2 moles of potassium in 1 mol of potassium sulfate.
1 mol of potassium will be there in 0.5 mol of potassium sulfate.
Mass of potassium is 4.15 g, molar mass is 39.1 g/mol.
Number of moles can be calculated as follows:

Here, m is mass and M is molar mass
Putting the values,

Thus, number of moles of
will be
.
The volume of solution is 225 mL, converting this into L,

Thus,

Putting the values in equation (1),

Therefore, concentration of potassium sulfate solution is 0.236 M.