It would be an physical change ; if you melt butter the butter goes from a solid to a liquid so therefore the physical state is changed.
<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.
<span>Scientific endeavors is basically all the things that would contribute to the process of achieving a certain scientific knowledge, from the initial observation, up to the point until we can hold that certain thing as acknowledged truth. So,
All scientific endeavors are supported by evidence.
All scientific endeavors are a systemic process.
All scientific endeavors involve observation.
All scientific endeavors involve experimentation.
All scientific endeavors involve the collection of information.
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