efficiency= [useful energy transferred ÷ total energy supply]×100%
So, [5500÷10000]×100%=0.55×100
=55%
Scientific Consensus is primarily a position, judgment, or a opinion of scientist in a particular area of there studies. So more or less like a opinion of the matter, its like saying, I don't agree with your study, and I think it should have been done another way.
The correct answer would be B. It is the compound Na2S that forms an ionic bond from the given ion above. From the choices, it is the only compound that exist and is available. Metals cannot react with another metal as well as nonmetal to nonmetal.
It will be a little bit less because of evaporation i learned that in third grade and your in high school that is sad