The puffed up appearance of dough is due to the production of which o…

The correct answer is Option (4) → CO₂ gas

Dough is fermented by microbes: the dough for dosa and idli by bacteria, and the dough for bread by baker’s yeast (Saccharomyces cerevisiae). As they break down the sugars in the dough, these microbes give off carbon dioxide. The gas collects as small bubbles inside the dough and makes it rise.

Option (1) SO₂ gas — Incorrect. Sulphur dioxide is not a product of the fermentation of dough. The microbes in dough release carbon dioxide.

Option (2) O₂ gas — Incorrect. The microbes in fermenting dough do not give off oxygen; producing oxygen is a feature of photosynthesis, not of fermentation.

Option (3) Water vapour — Incorrect. The rising of dough is caused by a gas made by the microbes. Water vapour is not the gas they release.

Option (4) CO₂ gas — Correct. During fermentation the bacteria and yeast release CO₂. The bubbles of this gas give the dough its puffed-up look.

NCERT Extract:
Microbes in Household Products – “… The dough, which is used for making foods such as dosa and idli is also fermented by bacteria. The puffed-up appearance of dough is due to the production of CO₂ gas. … Similarly the dough, which is used for making bread, is fermented using baker’s yeast (Saccharomyces cerevisiae).”