The Roman numerals are used to show the oxidation number of some transition metals because some elements have more than one possible oxidation state. So basically it's there to indicate the charge of the element.
72 percent is hydrogen. Nuclear fusion converts hydrogen into other elements. The sun is also composed of about 26 percent helium and trace amounts of other elements; oxygen, carbon, neon, nitrogen, magnesium, iron and silicon.
http://www.space.com/17170-what-is-the-sun-made-of.html
<u>a) Answer: </u>
<em>Number of molecules in 1 mole</em>
<u>Explanation:</u>
a) Whether we take any of the substance among all three of the given substances they will have the same number of molecules in 1 mole of the substance is considered and the value for this will be 
<u>b) Answer: </u>
<em>In the given question </em><em>mass of the substance</em><em> which is </em><em>greatest</em><em> is asked for </em><em>one mole</em><em> and we also know that </em><em>mass of one mole is given by molar mass. </em>
<u>Explanation:</u>
b) It is known that 
is the molar mass for oxygen which is greater than that of hydrogen while fluorine has a molar mass of 
which on comparison shows that, it is the highest amongst all three.
Answer:
A simple microscope is one that uses a single lens for magnification, such as a magnifying glass while a compound microscope uses several lenses to enhance the magnification of an object. It uses a lens to enlarge an object through angular magnification alone, giving the viewer an erect enlarged virtual image.
If its wrong correct me.
I believe the answer is C !
