Initially, when scientists were first using the taxonomy system to classify living organisms there were only considered to be 2 kingdoms: plants and animals. However, when the microscope was invented, scientists were able to observe differences in organisms at the cellular level! They were also able to observe microscopic living organisms like bacteria that they had not been able to observe before. Scientists realized it was necessary to add 4 new kingdoms to account for the observations they had not seen before the invention of the microscope.
Answer : A metal in group 16 of the periodic table can become a chemically stable ion by gaining 2 electrons.
Explanation :
The group 16 element are oxygen, sulfur, selenium, tellurium and polonium.
The general electronic configuration of group 16 elements is, 
As we now that there are total 6 electrons in p sub-shell. So, a metal in group 16 can become a chemically stable ion by gaining 2 electrons.
Hence, a metal in group 16 of the periodic table can become a chemically stable ion by gaining 2 electrons.
Answer:
No viruses are not considered as living organisms, until they enter the body of the host
D Energy input from the environment is stored in food molecules
during photosynthesis.
its correct.
