Which of the following is a disadvantage of glass?

The correct answer highlights a notable disadvantage of glass, which is its high melting point. While this property can be seen as an advantage in certain contexts, it presents challenges in manufacturing and processing. Glass tends to require significant energy and specialized equipment to reach its melting point, making processes such as molding or reshaping costly and complex. This aspect can limit the design and production flexibility compared to materials with lower melting points, like various plastics.

In contrast, materials characterized by lower melting points (such as certain polymers) are often easier to work with in product design and manufacturing, allowing for more efficient production and potential cost savings. This attribute makes glass less favorable in applications where quick production or recycling is necessary.

Considering the other options, glass's scratch resistance compared to polymers varies, but it is generally recognized that glass is quite scratch resistant, and for durability, it often excels. In terms of weight, glass is typically heavier than most common plastics, and while it offers some thermal properties, options that specifically reference thermal insulation also tend to favor plastics for being more effective in that category. Therefore, the high melting point stands out as a significant disadvantage during manufacturing processes.