the first ste in dark reaction of photosynthesis is

1. formation of ATP
2. excitation of chlorophyll molecule
3. photolsis of water
4. attachment of carbon dioxide to a pentose sugar

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Correct answer is 4. attachment of carbon dioxide to a pentose sugar.
The first step in dark reaction of photosynthesis is carboxylation. in which six molecules of carbon dioxide combine with six molecules of carbon dioxide combine with six molecules of ribulose 1, 5- biphosphate (RuBP) to form six molecules of unstable six carbon compound, Carboxylation of RuBP is catalysed and the enzyme RuBP carboxylase or RUBISCO.