Helium was discovered in 1868.
Answer:
The corona shines only about half as brightly as the Moon and is normally not visible to the unaided eye, because its light is overwhelmed by the brilliance of the solar surface. During a total solar eclipse, however, the Moon blocks out the light from the photosphere, permitting eye observations of the corona.
Water is called a universal solvent because of its ability to dissolve different types of substances.
The basic unit of life is cell and a large portion of living cell (60%) is made up of water, this is because cells need water to survive. Biochemical reactions are always ongoing in the living cells and water act as solvents under which these reactions occur. Because of the high solubility of water, it is able to dissolve various substances needed by the body, this makes it easy for the substance to participate in chemical reactions and to move from one point to another. Without water biochemical reactions will not be able to occur in cells and this will lead to the death of the cells.
What are the sentences?
It would help to see the sentences.
<span> First you need to know how many isotopes there are of silicon, and its average atomic units (look at periodic table). Then make up a system of equations to solve for it. Theres 3 stable silicon isotopes (28, 29, 30) so you will need to have 3 equations. You must be given the percent abundance of at least one of the isotopes to solve because here I can only see 2 equations (numbered down below) set x = percent abundance of si-28 y = percent abundance of si-29 z = percent abundance of si-30 since all of silicon atoms account for 100% of all silicon: x + y + z = 100% = 1 therefore: 1) x = 1 - y - z You also have 2) 28x + 29y + 30z = average atomic mass you can substitute x so that equation becomes: 28 (1 - y - z) + 29y + 30z = average atomic mass See how you have 2 variables here? You cant go on until you know the value of one isotope already or you have given a clue which you can derive the third equation</span>
