Hydrogencarbonate indicator changes colour according to the concentration of carbon dioxide present. The table shows how hydrogencarbonate indicator changes colour. colour of hydrogencarbonate indicator | concentration of carbon dioxide orange | atmospheric carbon dioxide concentration yellow | higher than atmospheric carbon dioxide concentration purple | lower than atmospheric carbon dioxide concentration Four test-tubes were set up under different conditions. The colour of hydrogencarbonate indicator in each test-tube at the start of the experiment and after 1 hour is also shown. Which test-tube shows that the rates of photosynthesis and respiration are the same?

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