Consider the following statements about the properties of perfect non reacting gas mixtures:

1) The total volume of a mixture is the sum of partial volumes at the same pressure and temperature.

2) The entropy of a mixture of gases is the sum of the the entropies of the constituents.

3) The total pressure of a mixture of gases is the sum of the partial pressures of the substances.

4) The mole fraction of a mixture of gases is equal to both pressure and volume fraction.

Which of the above statements is/are correct?