Geo-Scientist Prelims 2021 Chemistry Q33: A student calculated the pH of 10⁻⁷ M NaOH solution and 10⁻⁸ M HCl…

A student calculated the pH of 10⁻⁷ M NaOH solution and 10⁻⁸ M HCl solution to be 7 and 8, respectively. To verify, the student performed experiment in laboratory using pH-meter. The instrument displays the pH of former and later solutions as 7.3 and 6.9, respectively. Choose the correct answer from the following:

1. (a) The pH-meter is malfunctioned and the calculation results of the student are correct
2. (b) The pH-meter is working properly and the calculation results of the student are incorrect
3. (c) The pH-meter is malfunctioned and the calculation results of the student are wrong
4. (d) The calculation results of the student are correct and the instrument is working properly only for acids