Statement I: A thermos flask is made of double- walled glass bottles. Statement II: Metals are good conductors while gas and air are poor conductors of heat.

Statement I is true as a thermos flask, also known as a vacuum flask, consists of a double-walled glass vessel. Statement II is also true because metals are good conductors of heat due to their molecular activity, while gases like air are poor conductors (insulators) [2]. However, Statement II is not the correct explanation for Statement I. The primary reason for the double-walled construction is to create a vacuum between the walls. This vacuum is the 'best insulator' because thermal conduction requires the presence of matter; by removing air, heat transfer via conduction and convection is minimized. While the insulating properties of air are relevant in other contexts, the thermos specifically relies on the absence of air (vacuum) and the low thermal conductivity of glass to maintain temperature.

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 4: The World of Metals and Non-metals > Activity 4.3: Let us investigate > p. 47
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Conduction > p. 282