Question

What feature of double-glazed windows makes them good insulators? a. Thick glass is highly viscous. c. Heat conduction cannot take place through solid glass b. There is a vacuum between the panes of glass d. Thermal energy is not transferred through the special chemical glazing.

Answer 1

none of the above.
The air gap between the panes adds some thermal insulation.
About 1/2" is best. Less than that you get conduction. More than that you get more convection between panes. Double glazed windows do not usually have a vacuum in them -- there could be argon tho...