Statement A: Zeroth law of thermodynamics gives the concept of temperature. Correct. The Zeroth law states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This law establishes temperature as a fundamental state variable that determines whether systems are in thermal equilibrium. Statement B: First law of thermodynamics gives the concept of internal energy. Correct. The First law is essentially the law of conservation of energy applied to thermodynamic systems. It introduces the state function, internal energy ( $U$ ), through the relationship $\Delta Q=\Delta U+\Delta W$. Statement C : In isothermal expansion of an ideal gas, $\Delta Q \neq \Delta W$. Incorrect. For an isothermal process (constant temperature) involving an ideal gas, the change in internal energy ( $\Delta U$ ) is zero because internal energy depends only on temperature for an ideal gas. According to the first law ( $\Delta Q=\Delta U+\Delta W)$, since $\Delta U=0$, it follows that $\Delta Q=\Delta W$. Statement D: Product of intensive and extensive variables is extensive. Correct. An extensive variable depends on the amount of matter (e.g., mass, volume), while an intensive variable does not (e.g., pressure, temperature). Example: Pressure ( $P$ - intensive) × Volume $(V$ - extensive $)=$ Work $(W$ - extensive $)$. This holds true in general: Multiplying a quantity that scales with size by a constant (intensive) property results in a quantity that still scales with size. Statement E: The ratio of any extensive variable to mass will be an extensive variable. Incorrect. The ratio of an extensive variable to mass creates a specific property, which is intensive. Example: Volume (V-extensive) / Mass (m-extensive) = Specific Volume ( $v$ intensive). Because the ratio cancels out the dependency on the amount of matter, the result is intensive. Conclusion Based on our analysis, statements A, B, and D are correct.