Q.Which one gas is most abundant out of the four commonest greenhouse gases? Discuss the effect of this gas on the growth of plants?

Step 1. The chapter's greenhouse-gas contribution chart ranks CO2 at 60%, methane (CH4) at 20%, CFCs at 14%, and other gases (including N2O) at 6%, making CO2 clearly the most abundant contributor among the four commonest greenhouse gases.

Step 2. CO2 is essential as the raw material for photosynthesis, so plants require it to build sugars and grow, but the chapter's 'Global Warming Effects on Plants' list shows that excess atmospheric CO2 and the warming it drives disrupts plant growth rather than simply boosting it.

Step 3. Specific effects listed include low agricultural productivity in the tropics, more frequent heat waves that favour weeds, pests and fungi over crops, increased vector-borne plant diseases, storm and flood damage, water crisis and reduced irrigation, shifted flowering seasons and pollinator mismatch, altered species distribution ranges, and in extreme cases species extinction. …

Read the relative-contribution figures to identify the most abundant gas, then draw on the 'Global Warming Effec …

• Naming methane instead of CO2 as most abundant by confusing 'most potent per molecule' with 'most abundant by contribution'. …