The formula for calculating the amount of solute needed to prepare a solution of a specific concentration is:

```

Moles of solute = Molarity (M) × Volume of solution (L)

```

In this case, we want to prepare 1L of a 0.25 M solution of HCl. So, the moles of HCl needed are:

```

Moles of HCl = 0.25 M × 1 L = 0.25 moles

```

Step 2: Determine the mass of HCl needed.

The molar mass of HCl is 36.46 g/mol. So, the mass of HCl needed to prepare 0.25 moles of solution is:

```

Mass of HCl = Moles of HCl × Molar mass of HCl

= 0.25 mol × 36.46 g/mol = 9.115 g

```

Step 3: Prepare the solution.

- Add 9.115 g of HCl to a 1L volumetric flask.

- Add approximately 500 mL of deionized water to the flask.

- Swirl the flask gently to dissolve the HCl.

- Add more deionized water until the volume reaches the 1L mark.

- Mix the solution thoroughly.

The resulting solution will be 0.25 M HCl.