Which of the following statements describes why ion exchange of 99% SiO2 - 1% B2O3 in a salt bath of molten postassium chloride (KCl) is not an effective way to increase the surface strength of the glass sample?

The ion exchange works correctly, however both air-cooling and water-quenching are more efficient ways to induce a surface strengthening effect.

The glass is composed of only 1% B2O3, which is not a large enough proportion of B2O3 to undergo ion exchange, and therefore does not increase the surface strength of the sample effectively.

The potassium ion is smaller than B2O3, so when ion exchange takes place the surface is actually being weakened instead of strengthened.

The sample described above is composed of SiO2 and B2O3. Neither of these components are network modifiers, so ion exchange does not take place to strengthen the surface of the glass.

The surfaces of the glass sample are not cooled quickly enough to create a high internal strain energy that leads to strong surfaces.

The correct statement that describes why ion exchange of 99% SiO2 - 1% B2O3 in a salt bath of molten potassium chloride (KCl) is not an effective way to increase the surface strength of the glass sample is:

The ion exchange works correctly, however both air-cooling and water-quenching are more efficient ways to induce a surface strengthening effect.

Explanation:
Ion exchange is a process in which ions in a material are replaced with other ions from a surrounding medium. In the case of the glass sample described, the 99% SiO2 - 1% B2O3 composition means that the glass primarily consists of SiO2 with only a small proportion of B2O3.

In ion exchange, the small B2O3 ions are replaced by larger ions, such as K+ from the potassium chloride salt bath. This ion exchange process can lead to compressive stress on the surface of the glass, which can increase the surface strength and resistance to cracking.

However, in this case, the statement mentions that air-cooling and water-quenching are more efficient ways to induce surface strengthening. This implies that the ion exchange process in the salt bath with potassium chloride is not as effective in increasing the surface strength compared to cooling methods.

Air-cooling involves allowing the glass sample to cool naturally in air, while water-quenching involves quickly plunging the sample into cold water. Both of these methods create a high internal strain energy within the glass, resulting in strong surfaces.

Therefore, the statement correctly explains that while the ion exchange in the salt bath may work, it is not as effective as air-cooling or water-quenching in increasing the surface strength of the glass sample.