Answer : Option B) Plant stomata opening and closing to maintain homeostasis.
Explanation : Claude Bernand was a French Physiologist who first discovered about "homeostasis" which is defined as the controlled stability of the internal milieu, or internal environment, of cells and tissues in plants.
In plants stomatal opening and closing was done for maintaining homeostasis with the external and internal plant environment.
The percent by volume of a solution : 19.23%
<h3>Further explanation</h3>
Given
50 ml of ethanol
210 ml of water
Required
The percent by volume of a solution
Solution
Percent Volume (% v/v) : volume (ml) of solute/100 ml of solution ⇒ ratio of the volume of the solute to total volume of the solution

solute= Ethanol
solvent=water
Solution = solute+solvent
Total volume of the solution :

Percent by volume :

It's simple.
the number of protons in an atom never changes. And also, the no of protons is its atomic number.if you look up the periodic table, you will find a number on the top - left corner of each of the boxes. This is the atomic number.No 2 same elements on the periodic table have the same atomic number. So, all you have to do is search for a box that has the number 13 on it.
and by the way ... the element which you're searching for is Aluminium
Octet rule (quizlet helps)