A glass of composition 85% SiO2 - 15% K2O is to be surface strengthened by ion exchange. To this end, two identical specimens approximately the size and shape of credit cards are soaked for the same amount of time at 850 ∘C. Sample A is soaked in NaCl and sample B is soaked in KCl. From the list below, select the statements that are true.

a) The yield strength of Sample A will decrease while the yield strength of Sample B will increase.
b) The yield strength of Sample A will increase while the yield strength of Sample B will decrease.
c) The yield strength of both Samples A and B will increase.
d) The yield strength of both Samples A and B will decrease.
e) The yield strength of Sample A will decrease. There will be no change in the yield strength of Sample B.

It's e. The last one.

Thank u : D

To determine the effect of ion exchange on the yield strength of the glass specimens, we need to consider the composition and the ions involved in the exchange process.

In the given scenario, Sample A is soaked in NaCl, while Sample B is soaked in KCl. We also know that the glass composition is 85% SiO2 and 15% K2O.

When ion exchange occurs, the Na+ ions from the NaCl solution will replace some of the K+ ions in Sample A, while the K+ ions from the KCl solution will replace some of the Na+ ions in Sample B.

Now, let's analyze the statements:

a) The yield strength of Sample A will decrease while the yield strength of Sample B will increase.
This statement is false. Since Sample A is soaked in NaCl and some of the K+ ions are replaced by Na+ ions, it is expected that the yield strength would decrease. However, in Sample B, the K+ ions are replaced by K+ ions from the KCl solution, leading to a negligible change in the yield strength.

b) The yield strength of Sample A will increase while the yield strength of Sample B will decrease.
This statement is false, as explained in the previous analysis.

c) The yield strength of both Samples A and B will increase.
This statement is false. While the yield strength of Sample A is expected to decrease due to ion exchange, the yield strength of Sample B is not significantly affected.

d) The yield strength of both Samples A and B will decrease.
This statement is partially true. The yield strength of Sample A is likely to decrease due to ion exchange. However, the yield strength of Sample B is not significantly affected.

e) The yield strength of Sample A will decrease. There will be no change in the yield strength of Sample B.
This statement is true. As explained earlier, Sample A is expected to have a decreased yield strength due to the replacement of K+ ions with Na+ ions. Sample B, on the other hand, is not significantly affected.

Therefore, the correct answer is:
e) The yield strength of Sample A will decrease. There will be no change in the yield strength of Sample B.