A plant may not exchange Co2 or O2 with air at 1. Twilight 2. Midnight 3. Late hours in morning 4. Noon

Dear student,     
Please find below the solution to the asked query      

The correct answer is (a) i.e. twilight.

As we know, the rate of respiration is high at midnight while during late hours in morning and in the noon, the rate of photosynthesis is high. So, exchange of gases is definitely there during these times.
But, there are certain times, for example, twilight (soft light found between the period of sunlight and darkness), there occurs a transition between the two processes (respiration and photosynthesis). Hence, there is no net exchange of gases (CO2 and O2).

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