ANS:A - 'Reduced temperature' of a substance is the ratio of its existing temperature to its critical temperature, both expressed on celsius scale.

The wrong statement is: "Reduced volume is the ratio of the existing molal volume of a substance to its critical molal volume." The correct statement should be: "Reduced volume is the ratio of the existing volume of a substance to its critical volume." The reduced volume is a dimensionless quantity used in thermodynamics, particularly in the study of phase transitions. It is defined as the ratio of the actual volume of a substance to its critical volume. Therefore, the correct answer is: none of these.