The browning of fruit involves enzymes. The time taken for slices of apple kept in different solutions to turn brown is shown in the table. The effect of pH and sodium chloride concentration was investigated. All other variables were kept constant.
A student used the data to make the following statements about these enzyme-catalysed reactions.
Which of these statements is/are correct?
1 The enzymes involved in browning are denatured in weakly alkaline conditions.
2 The optimum pH for the enzymes is pH 7.0.
3 The enzymes are activated by sodium chloride.

Answer:

5) A

Let us first identify the most favourable conditions for the enzymes. To do this, we need to recognise the least time it took for the fruit to turn brown. 6 minutes. Two combinations of conditions resulted in the fruit turning brown in 6 minutes:
First combination = 7.0 pH and 0.0 NaCl conc. (neutral pH)
Second combination = 9.0 pH and 0.0 NaCl conc. (weakly alkaline pH)
Between these two pH, we cannot distinguish which one is more favourable, neutral pH or weakly alkaline pH. So statements 1 and 2 are false.
The 5th apple slice was placed in pH 7.0 and NaCl conc 0.5
It took 15 minutes for the slice to turn brown. If the enzymes were activated by NaCl, it should have taken less time to turn brown compared to slice 3 (pH 7.0 and 0.0 NaCl conc). Since it took more time, it means that the enzymes must be deactivated. So statement 3 is false.