Answer:
protons is 7 neutrons should be 9
Explanation:
protons number is its atomic number
the number of protons and the number of neutrons determine an element's mass number.
The best and most correct answer among the choices provided by your question is the fourth choice or letter D. Reptiles are the most critically endangered animal group. Their population is threatened due to illegal activities done by man like poaching.
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<u>Answer:</u>
Cyanobacteria start producing pure oxygen around 200 million years ago.
<u>Explanation:</u>
Many scientists believed that Earth did not have any oxygen. Cyanobacteria or the blue green algae are the microbes which produced oxygen for the first time with the help of photosynthesis. This was around 4.5 billion years ago: after Hadean eon.
They were very simple, but they produced oxygen in the early earth’s atmosphere. So, they brought evolution on earth. This “blue-green algae” exists in salt water, rocks and soils and play a major role in maintaining the ecosystem.