<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.
Electronegativity
Atomic radius
Ionization energy
Explanation:
The scientific notation:

where
and k is integer.
We have the example:

You can write the numbers in a "normal" form:

Make the sum:

And next write it in the scientific notation:

<h3>Other method:</h3>
You can add numbers in scientific notation if the power of tens in both number is the same.
Therefore you must convert the first number:

Now, you can make the sum:

Answer: Therefore, the volume of a 0.155 M potassium hydroxide solution is 56.0 ml
Explanation:
Molarity of a solution is defined as the number of moles of solute dissolved per Liter of the solution.
According to the neutralization law,
where,
= molarity of
solution = 0.338 M
= volume of
solution = 25.7 ml
= molarity of
solution = 0.155 M
= volume of
solution = ?
= valency of
= 1
= valency of
= 1
Therefore, the volume of a 0.155 M potassium hydroxide solution is 56.0 ml