• # question_answer                         The given graph shows different levels of oxygen in the air at different times in a park. Which point (W, X, Y or Z) on the graph, shows the level of oxygen in the air at night? A)  W                               B)  X                    C)  Y                    D)         Z

Plants give out$C{{O}_{2}}$and take in${{O}_{2}}$during respiration whereas they give out${{O}_{2}}$and take in $C{{O}_{2}}$during photosynthesis. At daytime photosynthesis exceeds respiration hence${{O}_{2}}$is released but at night photosynthesis stops and $C{{O}_{2}}$is released from plants. That is why level of oxygen will decline during night. In the given graphs, 'Y' shows concentration of ${{O}_{2}}$in the air at night.