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.
Answer : The value of rate constant is, 
Explanation :
First we have to calculate the rate constant, we use the formula :
Expression for rate law for first order kinetics is given by:

where,
k = rate constant = ?
t = time passed by the sample = 20 min
a = let initial amount of the reactant = 100 g
a - x = amount left after decay process = 100 - 85 = 15 g
Now put all the given values in above equation, we get


Therefore, the value of rate constant is, 
Answer:
ionic bond
Explanation:
calcium is a metal and oxygen is a nonmetal. Ionic bonds occur between a metal and a nonmetal while covalent bonds occur between two nonmetals.
B. Adjusted that is your answer
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Answer:
The correct option is;
(B) 1 s², 2s², 2p⁶, 3s², 3p³
Explanation:
The electron configuration is the outline of the electron arrangement about a nucleus
In the systemic pattern of electron arrangement within an atom, there are, s, p, d, f orbitals
The maximum number of electrons in an s, p and d orbital = 2, 6, and 10 respectively
Based on Aufbau's principle the electrons are arranged based on the order of their energy level
The charge is presented by the number of electrons in the outermost shell, an element able to form an ion of charge of -3 will gain 3 electrons to complete its outermost shell
Among the options given, option B is the only option that has the capacity to take the electrons to complete the number of electrons in the p orbital outermost shell to 6 from 3, that is 3p³ + 3e⁻→ 3p⁶.