Question

plants take co2 and release oxygen in morning and why they take Oxygen and release co2 in night time

Answer 1

Plants carry out photosynthesis as well as respiration during daytime. During photosynthesis they take in carbon dioxide and give out oxygen (by product of photosynthesis) and at the same time they also emit carbon dioxide and take in oxygen for respiration. But the amount of oxygen emitted is greater.
While in the night, there is no sunlight available for photosynthesis; hence no oxygen can be produced. So the only process which goes on is respiration in which carbon dioxide is released.