Which statement about glass types is correct?

• A. Type I glass has a lower thermal coefficient of expansion relative to Type II and Type III glass.
• B. Type II and Type III glass have lower melting point than Type I glass therefore they are easier to mold into various shapes.
• C. Boric oxide is responsible to the chemical resistance, or resistance to leaching of Type II glass.
• D. Two of the above

Answer: (D)

The main idea here is how glass composition influences two practical properties: how much it expands with heat and how easily it can be melted and formed. Type I glass is borosilicate, which makes its network very strong and tightly connected. That tight structure gives a small coefficient of thermal expansion, so it changes size very little with temperature changes. In contrast, the soda-lime glasses used for Type II and Type III have looser networks and thus expand more when heated.

For melting and molding, Type I borosilicate requires higher temperatures to soften because of that strong network, while Type II and Type III, being soda-lime glasses, melt or soften at lower temperatures. So they’re easier to mold.

Regarding chemical resistance, boric oxide is a key component that boosts chemical durability in borosilicate glass, but that property is not what Type II glass relies on. Type II’s improved chemical resistance comes mainly from its composition and any surface treatments, not boric oxide content. So the two statements that are correct are that Type I has a lower thermal expansion, and that Type II and Type III have lower melting points (making them easier to mold). The claim about boric oxide being responsible for Type II’s chemical resistance isn’t accurate.