Molarity and Molality:
Molarity and molality are both units of concentration used to describe the amount of solute in a solution. However, they differ in their definitions and units of measurement.

1. Molarity (M): Molarity is defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (mol/L or M). Molarity is a commonly used unit of concentration in chemistry.

2. Molality (m): Molality is defined as the number of moles of solute per kilogram of solvent. It is expressed in moles per kilogram (mol/kg or m). Molality is used when the temperature of the solution is not constant, as it does not depend on the volume of the solution.

Given Information:
- Molarity of the solution = 2M
- Molality of the solution = 2.5m

Calculating Weight of Solvent:
To find the weight of the solvent present in the 1-liter solution, we need to convert the given information into a usable form.

1. Molarity (M):
The molarity of a solution is given as 2M, which means there are 2 moles of solute present in 1 liter of the solution.

2. Molality (m):
The molality of a solution is given as 2.5m, which means there are 2.5 moles of solute present in 1 kilogram of the solvent.

Conversion:
To convert the given information into a usable form, we need to know the molar mass of the solute. Without this information, it is not possible to calculate the weight of the solvent.

Let's assume the molar mass of the solute is 'X' g/mol.

We know that:
- Molarity (M) = moles of solute / volume of solution in liters
- Molality (m) = moles of solute / mass of solvent in kilograms

Using the given information and the conversion factors, we can set up the following equations:

1. Molarity (M):
2M = 2 moles of solute / 1 liter of solution

2. Molality (m):
2.5m = 2.5 moles of solute / (mass of solvent in grams / 1000)

In order to proceed with the calculation, we need the molar mass of the solute.

Conclusion:
Without the molar mass of the solute, it is not possible to calculate the weight of the solvent present in the 1-liter solution. The answer cannot be determined with the given information.